Optical  Dictionary 

AND 

Encyclopedia 

THIRD    EDITION 

LEWIS 


REVISED  MAY  i,  1909 


U,C,1PP.EY  LIBRARY 


imm/ 


1^^ 


POCKET 

Optical   Dictionary 


INCLUDING 


Pronunciation  and  Definition 


WORDS 


Optometry   and   Oplitkalmology 


Together  with  a  complete  description 
of  the  light  wave  theory,  Anatomy  of 
the  Eye,  functions  and  nerve  supply 
of  the  different  parts,  Retinoscope, 
Ophthalmoscope,  Trial  Case  and  how 
to  use  them.  Transposition,  Toric 
and  other  lenses. 


By  JAMES  J.  LEWIS,  Opt.  D. 

Professor  of  Optometry  in  the  Northern  Illinois  College  ol 
Ophthalmology  and  Otology. 


THIRD  EDITION 
Revised   and   Enlarged  Illustrated 


Copyrigkt,  J.  J.  LEWIS 
1908 


M 


OPTO 


To  the  Public: 

This  edition  has  been  compiled  with  a 
great  deal  of  care.  Realizing  that  perfection 
in  its  full  sense  hasi  never  been  attained  by 
mortal  man,  the  author  invites  the  unbiased 
and  conscientious  criticism  of  the  readers  and 
users  of  this  Dictionary  and  hereby  earnestly 
solicits  the  same  to  the  end  that  the  future 
editions  may  profit  by  the  honest  convictions 
of  studious  oculists,  physicians  and  optome- 
trists. 

I  cannot  conclude  -without  expressing  my 
deep  sense  of  obligation  to  the  profession  for 
their  kind  reception  of  this  work.  Feeling 
the  responsibility  incurred  by  those  who 
attempt  to  teach  others,  I  have  spared  no 
amount  of  labor  or  cost  to  render  this  volume 
clear,  practical  and  useful. 

Very  respectfully. 

The  Author. 


bKE 


Z.[ 


PREFACE 

TO  THE  THIRD  EDITION 


^  P  <  The  second  edition  of  this  work  has  met 
with  so  much  favor,  that  the  Author  has 
attempted  to  revise  it,  and  in  this  way  make 
it  more  worthy  of  the  commendation  of  the 
profession.  Many  definitions  have  been  re- 
written, and  about  twenty  pages  of  new 
matter  has  been  added  in  the  form  of  an 
appendix. 

I  wish  to  express  my  appreciation  for  the 
efficient  assistance  extended  by 

J.  B.  McFatrich,  M.  S.,  M.  D., 

Professor  of  the  Principles  of  Ophthalmology 

and  Otology. 

Geo.  Wilbur  McFatrich,  M.  D., 

Professor  of  Clinical  and  Didactic  Ophthalmology 
and  Otology. 

Henry  S.  Tucker,  A.  M.,  M.  D., 

Professor  of  Anatomy  and  Physiology  of  the  Eye 
and  Brain. 

I  particularly  acknowledge  the  assistance 
of  my  friend.  Dr.  G.  W.  McFatrich,  whose 
knowledge,  gained  through  experience  as  Pro- 
fessor of  Ophthalmology  in  Medical  Colleges 
and  as  Oculist  to  Hospitals  in  Chicago  and 
large  professional  practice  in  Diseases  of  . 
the  Eye,  has  been  freely  placed  at  my  com- 
mand in  bringing  this  little  book  to  the 
highest  possible  standard. 

J.  J.  Jm 


ABBREVIATIONS  AND   OPTICAL  SIGNS, 

Ace Accommodation. 

Aet Age. 

Am Ametropia. 

An Anisometropia. 

As Astigmatism. 

Asth Asthenopia. 

Ax Axis. 

Cc.  or  —  (minus) Concave. 

Ce Centigrade. 

Cm Centimeter. 

Cx.  or  +  (plus) Convex. 

Cyl Cylinder. 

D Diopter. 

D.  Cc Double  concave. 

D.  Cx Double  convex. 

D.  T Distance  test. 

E   or  Em Emmetropia. 

H.  or  Hy Hypermetropia. 

In Inches. 

L.  or  L.  E Left  eye. 

M.  or  My Myopia. 

Mm Millimeter. 

N Nasal. 

N V Naked  vision. 

O.  D.  (Oculus  Dexter) Right  eye. 

O.  S.  (Oculus  Sinister) Left  eye. 

O.  U.  (Oculi  Unati) Both  eyes. 

P.  or  Pb Presbyopia. 

P.  Cc Periscopic  concave. 

P.  Cx. Periscopic  convex. 

P.  D. . . .  ,  ♦  t ,  , ,  , ,  , Inter-Pupillary  distance. 


ABBREVIATIONS  AND  OPTICAL  SIGNS— Con. 

PI Piano. 

p.  p.  (Punctum  Proximum)Near  point, 
p.  r.  (Punctum  Remotum)  Far  point. 

Pr Prism. 

R.  or  R.  E Right  eye. 

R.  T Reading  test. 

Rx Prescription. 

Sb Strabismus. 

S.  or  Sph Spherical. 

T .Temporal. 

Ty Type. 

V .... Vision. 

Va Visual  acuteness. 

W.  P Working  point. 

+ Plus  convex. 

— Minus  — concave. 

O Combined  with. 

^ Degree. 

A Prism  Diopter. 

= .^ Equal  to. 

00 Infinity,  20  ft.  or  farther. 

'-" Line,  12th  part  of  inch. 


Should  the  word  not  be  found  in  alphabetical  order 
refer  to  the  appendix. 

When  this  sign  *  is  found  at  the  end  of  a  definition. 
refer  to  the  same  word  in  the  appendix. 


Lewis  Pocket  Optical  Dictionary. 


A-baxial  (ab-aks'-e-al).  Not  situate  in  the  line  of 
the  axis. 

Abducens  (ab-du'-senz).  Refers  to  the  sixth  pair  of 
nerves  that  control  the  movement  of  the  external 
rectus  muscles.  They  are  the  straight  muscles, 
sometimes  called  the  abducens  muscles,  located 
on  the  temple  side  of  the  eyeball,  which  turn  the 
eye  outward,  and  under  normal  conditions  these 
muscles  should  overcome  about  8  degrees  of 
prism,  base  in. 

Abduct.     To  draw  away  from  the  median  line. 

Abduction  (ab-duc'-shun).  The  act  of  turning  the 
eye  outward.  For  testing  the  power  of  the  ab- 
ductors or  external  recti  muscles,  use  the  strong- 
est prism,  base  in,  with  which  the  eye  can  over- 
come diplopia. 

Abductor  (ab-duc'-tor).  Any  muscle  that  abducts. 
For  instance,  the  external  rectus. 

Aberration  (ab-er-a'-shun).  Wandering  from  nor- 
mal. When  applied  to  lenses  would  mean,  unable 
to  obtain  a  perfect  focus.  It  is  due  to  the  greater 
refractive  power  of  the  edge  over  the  center  of 
convex  lenses,  thus  causing  the  image  to  be  some- 
what blurred.  In  the  eye  the  iris  shuts  off  the 
edge  of  the  lens,  and  in  this  way  prevents  spherical 
aberration.  Chromatic  Aberration,  dispersion  of 
colors.  Owing  to  the  colored  rays  having  differ- 
ent degrees  of  refractibility  they  are  not  focused 
at  the  same  distanc  \ 


8  LEWIS  POCKET 

Ablatio-retinae  (ab-la'-she-o-ret'-in-e).  Detachment 
of  the  retina. 

Ablepharia  (ah-blef-ar'-e-ah).  That  condition  in 
which  the  eyeHds  are  absent. 

Ablepsia  (ah-blep'-se-ah).    BUndness — want  of  sight 

Abnormal.  Away  from  normal.  Relating  to  vision 
would  mean,  any  defect  of  sight.  (Ametro- 
pia.) An  eye  wherein  parallel  rays  of  light  do 
not  focus  on  the  retina  with  the  muscles  of  accom- 
modation at  rest. 

Abrasio-cornea  (ab-ra'-sio-cor'-ne-ah) .  The  rub- 
bing off  of  the  outer  layer  of  the  cornea. 

Abscess  (ab'-ses).  A  collection  of  pus  in  any  cavity 
formed  by  the  separation  of  tissue. 

Absolute  Index  of  Refraction  is  that  which  is  found 
when  light  passes  from  a  vacuum  into  a  given 
medium. 

Absorption  (ab-sorp'-shun) .  A  term  applied  in  the 
operation  for  cataract  where  the  lens  capsule  is 
needled,  allowing  the  aqueous  humor  to  absorb 
the  lens. 

Absorptive.  Anything  that  has  the  power  of  ab- 
sorption. 

V  Accommodation.  The  power  to  adjust  the  eye  to 
see  within  its  far  point.  It  takes  place  by  con- 
tracting the  ciliary  muscles  which  encircle  the 
lens  and  draws  forward  the  choroid  and  hyaloid 
membrane,  the  suspensory  ligaments  be- 
coming relaxed,  and  the  lens  (by  its  own  elas- 
ticity)  allowed  to  as.^ume  a  greater  convexity, 


\f 


OPTICAL  DICTIONARY.  § 

especially  its  anterior  surface,  thus  increasing  its 
refraction.  Amplitude  of  Accommodation  (from 
Landolt)  as  follows: 

Age  in  Amplitude 

Years  (dioptres) 

10 14 

15 12 

20 10 

25 8.5/ 

30.. 7.0 

35 5.5 

40 4.5 

45 3.5 

50 2.5 

55 . . , 1 .  75 

60 1.0 

65 0.75 

70 0.0 

This  is  approximately  correct,  but  individuals 
differ  in  the  amount  of  accommodation  they 
possess  at  the  same  age. 

Achroma.     Without  color. 

Achromatic  Lens  (ah-kro-matMk).     (See  Lens.) 

Achromatism  (ah-kro'-ma-tism).     Absence  of  chro- 
matic aberration. 

Achromatopsia  (ah-kro-mat-op'-se-ah).    Color-blind- 
ness. 

Achromatosis     (ah-kro-mat-o'-^sis).       Any     disease 
marked  by  lack  of  pigmentation. 

Acorea  (ah-ko'-re-ah).     When  the  pupil  is  absent. 
Acouired.     Ngt  hQvn  with,  but  developed  after  birth, 


10  LEWIS  POCKET 

f  Acuity  (ak-u'-it-e).  Sharpness,  like  a  needle.  The 
sharpness  of  vision;  the  keenness  of  the  visual 
powers.  The  acuteness  of  vision  means  the  vision 
the  patient  has  with  his  full  correction.  The 
faculty  of  the  retina  to  perceive  forms  depends 
on    many    conditions — 

1.  Primarily,  on  the  sensibility  of  the  retina. 

2.  On  the  adaptation  of  the  retina. 

3.  On  the  general  illumination. 

4.  On  the  sharpness  of  the  retinal  image. 

5.  On  the  intensity  of  the  illumination. 

It  is  known  that  the  acuteness  of  vision  varies 
with  the  general  illumination  up  to  a  certain 
degree  of  intensity,  as  that  of  a  clear,  sunny  day; 
the  two  then  vary  in  a  direct  proportion,  but 
when  the  illumination  passes  a  certain  limit  of 
intensity,  the  acuteness  of  vision  diminishes 
instead    of    increases. 

Adaptation  (ad-ap-ta'-shun).  Adjustment  of  the 
pupil  to  light. 

Adducens  (ad-du'-sens).  When  this  term  is  applied 
to  the  eye  it  means  the  internal  rectus  muscle, 
the  muscle  which  turns  the  eyeball  inward  toward 
the  nose.  The  power  of  adduction  of  the  eye 
ranges  from  twenty  up  to  fifty  degrees.  For 
testing  the  power  of  the  adducens  or  internal 
rectus  muscle,  use  the  strongest  prism,  base  out, 
with  which  the  eyes  can  overcome  diplopia. 


\ 


Adduct.     To  draw  inward  toward  a  center. 

Adduction.  Movement  of  the  eyeball  inward.  The 
adducens  means  the  internal  rectus  muscle  by 
which  we  turn  the  eyes  inward.  The  test  for  the 
power  of  the  adducens   is    made  by  placing  the 


OPTICAL  DICTIONARY.  li 

base  out  of  the  strongest  prism  with  which  the  eyes 
can  overcome  diplopia. 

Adenectomy  (ad-en-ek'-to-me).  Removal  of  a  gland 
by  operation. 

Adenemphraxis.  That  condition  in  which  the  duct 
or  gland  is  obstructed. 

Adenoid  (ad'-en-oid).      Resembling  a  gland. 

Adenophthalmia  (ad-en-off-thal'-me-ah) .  Inflam- 
mation of  the  meibomian  glands. 

Advancement.  The  cutting  away  of  a  muscle  of  the 
eye  and  attaching  it  to  an  advanced  point.  This 
operation  is  performed  on  the  weak  muscle  in 
cases  of  strabismus. 

Adventitious  (ad-ven-tish'-us).  Acquired— not  nor- 
mal. 

Albinism  (al'-bin-ism).  Abnormal  deficiency  of  pig- 
ment in  the  iris  and  choroid. 

Albugo  (al-bu'-go).  White  opacity  of  the  cornea  of 
the  eye.      Leukoma. 

Alexia  (a-lex'-ia).  Unable  to  read,  due  to  a  central 
lesion. 

Amaurosis  (am-aw-ro'-sis).  A  disease  of  the  optic 
nerve  or  retina,  which  causes  blindness. 

"^  Ambiopia  (am-be-o'-pe-ah).     Vision  with  both  eyes. 

.  Amblyopia  (am-ble-o'-pe-ah).  A  dimness  of  vision 
^  from  defective  sensibility  of  the  retina.  A 
condition  in  which  there  is  a  possibility  of  re- 
storing the  former  vision;  for  instance,  when  a 
person  has  an  error  of  refraction  in  one  eye,  the 
other  eye  being  emmetropic^  he  will  learn  to  ignore 
the  eye  with  the  error,  and  use  the  one  with  the 


12  LEWIS  POCKET 

best  vision.  In  this  way  the  sight  will  become 
dim  from  want  of  use,  and  is  an  acquired  state, 
which  by  testing  with  the  pinhole  disc  will  show 
no  improvement.  Under  these  conditions,  the 
error  must  be  corrected  with  the  retinoscope,  and 
if  the  eyes  are  not  more  than  two  diopters  apart  in- 
struct your  patient  always  to  wear  his  correction 
and  cover  the  good  eye  two  or  three  times  a  day, 
for  a  period  of  ten  minutes  at  a  time,  and  try  to 
use  the  amblyopic  eye.  In  this  way  you  will 
notice  an  improvement  each  week.  When  the 
pinhole  disc  fails  to  improve  vision,  the  eye  is 
either  amblyopic  or  in  a  diseased  state.  Toxic 
Amblyopia  is  a  dimness  of  vision  from  the  poison- 
ous effect  of  drugs,  such  as  quinine,  upon  the 
nervous  system — excessive  use  of  tobacco  or  al- 
coholic stimulants  produce  the  same  effect.  The 
treatment  for  this  form  of  Amblyopia  does  not 
consist  of  glasses,  but  the  patient  must  quit  the 
use  of  the  drug  causing  the  trouble,  and  if  not 
too  far  advanced  there  is  a  possibility  of  recov- 
ering the  former  vision.  A.,  Postmar'ital,  that  due 
to  sexual  excess.    A.,  Crossed,  on  one-half  of  retina. 

s|  Amblyopia  ex  Anopsia.  Amblyopia  resulting  from 
one  eye  having  been  excluded  for  some  time 
from  binocular  vision. 

Ametrometer      (a-met-rom'-e-ter) .     An  instrument 
used  for  measuring  ametropia. 

V    Ametropia      (a-met-ro'-pe-ah).     Any    error    of    re- 
fraction,  such    as    hyperopia,   myopia,   or    astig- 
matism. 
Amphice'lous.      Concave  on  both  sides  or  ends. 
Amphodiplopia   (am-f o-dip-lo'-pe-ah) .     That  condi- 
.XlQU  where  both  eyes  have  double  vision, 


I  OPTICAL  DICTIONARY  13 

Amplifier  (am'-ple-fi-er) .  An  apparatus  for  increas- 
ing the  magnifying  power  of  a  microscope. 

Amplitude  of  Accommodation.     The  power  or  force 
N    necessary  to  change  the  eye  from  its  far  point 
to  its  near  point  (or  from  its  punctum  remotum 
to   its   punctum    proximum).       (See    Accommo- 
dation.) 

Amplitude    of   Convergence.     The    power    or   force 
Ny^  necessary  to  turn  the  eyes  from  their  far  point 
to  their  near  point  of    convergence.     It  is  rep- 
resented by  the  greatest  number  of  meter  angles 
of  convergence  that  the  eyes  can  exert. 

Anacamptom'eter.  An  instrument  for  measuring 
the  reflexes. 

Anaclasis  (an-akMas-is).  When  this  term  is  applied 
to  Hght,  it  refers  to  the  rays  traveling  obliquely 
from  a  rarer  to  a  denser  media,  being  bent  back- 
ward toward  the  perpendicular  (refraction). 

Anaesthesia  (an-es-the'-ze-ah).  Lacking  sensitive- 
ness, where  the  retina  is  amblyopic. 

Anatomy  (an-at'-o-me)  (Eye).  Relates  to  the 
description  of  the  structures  of  the  eye  and  its 
parts.  The  eyeball  is  nearly  spherical  in  shape  and 
measures  about  24  mm.  in  diameter.  The  cornea 
represents  a  segment  of  a  small  sphere  projecting 
from  its  anterior  surface.  The  first  tunic  of  the 
eyeball  is  the  sclerotic  and  cornea.  The  posterior 
five-sixths  is  the  sclerotic,  which  is  white  and 
opaque,  and  serves  to  give  shape  to  the  eye  and 
protects  its  more  delicate  interior.  Near  the 
posterior  pole,  on  the  nasal  side,  is  a  sieve-like 
disc  known  as  the  lamina  cribrosa,  through  which 


14 


LEWIS  POCKET 


the  optic  nerve  fibers  enter  the  eye.  The  sclerotic 
is  thickest  at  its  posterior  portion  and  gradually 
becomes  thinner  as  it  approaches  the  equator, 
and  again  thickens  as  it  approaches  the  cornea. 
The  anterior  one-sixth  is  the  cornea.  It  is  trans- 
parent and  of  a  greater  curvature  than  the 
sclerotic.     The  cornea  is  set  in  the  sclerotic  as 


a  watch  crystal  is  placed  in  its  frame  and  is  com- 
posed of  five  layers.  From  without  inward  as 
follows:  Conjunctiva  Epithelium,  Bowman's 
membrane,  Cornea  proper,  Membrane  of  Desce- 
met,  and  the  Endothelium.  At  the  inner  angle 
(angle  of  filtration)  between  the  iris  and  cornea, 
there  are  a  number  of  comb-like  openings  which 
are  iu  the  trabecular  tissue  or  pectinate  ligament 


OPTICAL  DICTIONARY.  15 

which  runs  from  the  periphery  of  the  cornea  to 
the  base  of  the  iris.  These  openings  are  called 
the  spaces  of  Fontana,  through  which  the  aqueous 
humor  passes  into  the  canal  of  Schlemm,  a  cir- 
cular canal  extending  around  the  periphery  of 
the  cornea  at  the  sclero  corneal  junction,  but 
entirely  within  the  cornea.  From  this  canal  the 
humor  passes  into  the  anterior  ciliary  veins.  The 
second  tunic  of  the  eye  is  composed  of  the  choroid, 
ciliary  body  and  the  iris.  It  lines  the  inner  side 
of  the  sclerotic,  and  is  perforated  to  allow  the 
optic  nerve  to  enter,  and  has  a  circular  opening  in 
front,  which  is  known  as  the  pupil.  Through 
this  tunic  the  eye  obtains  its  principal  blood  and 
nerve  supply.  This  is  the  tunic  in  which  the 
pigment  is  deposited  for  the  purpose  of  absorbing 
light.  The  choroid  is  said  to  nourish  the  retina 
and  the  vitreous.  The  ciliary  muscles  are  within 
the  ciliary  body,  and  are  used  for  accommodating. 
The  iris  is  the  most  anterior  portion  of  the  second 
tunic.  It  is  located  in  front  of  the  crystalline 
lens,  and  separates  the  posterior  and  anterior 
chambers;  it  gives  the  eye  its  color,  regulates 
the  amount  of  light  which  enters,  and  prevents 
spherical  aberration  of  the  lens.  The  third  tunic 
is  the  retina.  It  is  a  very  delicate,  transparent 
membrane,  made  up  of  ten  layers,  one  of  which  is 
the  layer  of  optic  nerve  fibers.  These  fibers  pass 
through  the  lamina  cribrosa  at  the  optic  disc, 
and  flatten  out  more  and  more  as  they  approach 
the  front  of  the  eye.  The  retina  is  attached  in 
two  places,  at  the  optic  disc  and  at  its  anterior 
border,  the  ora  serrata.  It  is  not  attached  to 
the  choroid,  but  simply  lies  on  it.  In  examining 
the   retina   with    the    ophthalmoscope   you    will 


A  CUT  THROUGH  THE  CILIARY  BODY. 
,  Cornea;  Scl,  Sclerotic;  Ch,  Choroid;  R,  Retina;  or^  C 
Serrata;  Z,  Zonule  of  Zinn  or  Suspensory  Ligamen 
//,  Petit's  Canal;  p,  Edge  of  Pupil;  P,  the  most  promint 
part  of  the  Ciliary  Process;  sp,  Sphincter  Pupillae  Muse 
a,  Canal  of  Schlemm;  L,  Conjunctiva;  B,  Lens;  I,  Angle 
Filtration. 


OPTICAL  DICTIONARY.  17 

notice  the  optic  disc  on  the  nasal  side  which 
marks  the  entrance  of  the  optic  nerve  into  the 
globe.  The  macula  lutea,  which  is  the  most  sen- 
sitive spot  of  the  retina  (sometimes  called  the 
yellow  spot,  as  it  is  said  to  turn  yellow  after 
death),  is  situated  slightly  on  the  temple  side. 
The  functions  of  the  retina  are  to  receive  the  . 
impressions  of  the  waves  of  light  and  transmit 
them  through  the  optic  nerve  to  the  brain.  The 
space  between  the  iris  and  cornea  is  known  as 
the  anterior  chamber  of  the  eye,  and  that  between 
the  iris  and  the  lens  as  the  posterior  chamber. 
Both  of  these  chambers  are  filled  with  a  transpar- 
ent, watery  fluid  known  as  the  aqueous  humor. 
The  large  chamber  back  of  the  crystalline  lens  is 
known  as  the  vitreous  chamber,  and  contains  the 
vitreous  humor  which  occupies  a  little  more  than 
three-fourths  of  the  eyeball.  It  is  a  perfectly 
transparent  substance  about  the  consistency  of 
the  white  of  an  egg,  and  is  enclosed  in  a  thin  trans- 
parent sac  known  as  the  hyaloid  membrane.  This 
membrane  divides  at  the  ciliary  body  and  forms 
what  is  known  as  the  anterior  and  posterior  sus- 
pensory ligaments,  which  are  attached  to  the 
lens  capsule,  thus  forming  what  is  known  as 
Petit's  Canal  and  the  Zonule  of  Zinn.  Within 
the  lens  capsule  the  crystalline  lens  is  to  be  found. 
In  shape  the  lens  resembles  a  bi-convexed  lens, 
except  that  it  is  less  curved  in  front  than  behind; 
in  youth  it  is  highly  elastic,  moderately  firm,  yet 
a  perfectly  transparent  body,  as  clear  as  a  crystal, 
and  as  we  grow  older  it  becomes  harder  and 
sometimes  of  a  slightly  straw  tint.  The  crystal- 
line lens  is  made  up  of  layers  closely  resem- 
bling those  of  an   onion,  which  accounts  for  its 


18  LEWIS  POCKET 

elasticity.  The  eyeball  is  imbedded  in  the  fatty 
substance  of  the  orbit,  and  is  surrounded  by  a 
thin  membranous  sac,  which  isolates  it  and  at  the 
same  time  allows  free  movement.  This  sac  is 
named  the  Capsule  of  Tenon.  It  is  a  very  deli- 
cate membrane  consisting  of  two  layers  which 
invest  the  posterior  part  of  the  globe  from  the 
margin  of  the  cornea  backward  to  the  entrance 
of  the  optic  nerve,  and  is  connected  to  it  by  a 
very  delicate  connective  tissue.  Both  layers  are 
lined  on  the  inner  surface  by  endothelial  cells.  The 
cavity  between  them  is  continuous  with  the  space 
between  the  two  layers  of  the  sheath  of  the 
optic  nerve,  which  is  known  as  the  subarachnoid 
space.  The  inner  layer  is  known  as  the  pia  mater, 
and  the  outer  as  the  dura  mater,  and  between 
them  empty  the  lymphatic  vessels  of  the  sclerotic. 
This  capsule  is  penetrated  by  the  (tendon)  muscle,! 
of  the  eyeball  near  their  insertion,  which  spread 
out  fan  shape,  and  are  attached  to  the  sclerotic. 

Anatomist  (a-nat'-o-mist).     A  person  who  is  skilled 
in  anatomy. 

Anatomy  of  Orbits.  The  orbits  are  two  pyramidal 
I  cavities,  situated  at  the  upper  and  anterior  part 
of  the  face,  their  bases  being  directly  forward 
and  outward  and  their  apices  backward  and 
inward,  so  that  the  axes  of  the  two  if  continued 
backward  would  meet  over  the  body  of  the 
sphenoid  bone.  The  orbit  is  lined  with  perios- 
teum, the  periorbita.  Each  orbit  is  formed  of 
seven  bones,  the  frontal,  the  sphenoid,  ethmoid, 
superior  maxillary,  malar,  lachrymal,  and  palate; 
but  three  of  these,  the  frontal,  ethnoid,  and 
sphenoid,  enter  into  the  formation  of  both  orbits, 


\' 


OPTICAL  DICTIONARY.  19 

SO  that  the  two  cavities  are  formed  of  eleven 
bones  only.  The  orbital  opening,  or  mouth, 
is  called  aditus  orbitae  (Aditus  Orbitae — 
entrance  to  orbit).  At  the  apex,  or  back  part 
of  the  orbit  on  the  nasal  side,  is  a  small  circular 
opening  known  as  the  optic  foramen,  which  trans- 
mits the  optic  nerve  and  ophthalmic  artery. 
There  are  nine  openings  communicating  with 
each  orbit,  viz.,  the  optic  foramen,  the  spheno- 
maxillary fissure,  sphenoidal  fissure,  supraorbital 
foramen,  anterior  and  posterior  ethmoidal  for- 
amina, infraorbital  canal,  malar  foramina,  and 
the  canal  for  the  nasal  duct.  Spheno-maxillary 
fissure  transmits  the  superior  maxillary  nerve 
and  its  orbital  branches,  the  infraorbital  vessels, 
and  the  ascending  branches  from  the  spheno- 
palatine or  Meckel's  ganglion.  Sphenoidal  fissure 
transmits  the  third,  the  fourth,  the  three 
branches  of  the  ophthalmic  division  of  the  fifth, 
the  sixth  nerve,  some  filaments  from  the  cavern- 
ous plexus  of  the  sympathetic,  the  orbital 
branch  of  the  middle  meningeal  artery,  and  a 
branch  from  the  lachrymal  artery  of  the  dura 
mater,  and  the  ophthalmic  vein.  Supraorbital 
foramen  transmits  the  supraorbital  artery,  nerve 
and  vein^.  Anterior  ethnoidal  foramen  transmits 
the  anterior  ethmoidal  vessels  and  nasal  nerve. 
Posterior  ethmoidal  foramen  transmits  the  poste- 
rior ethmoidal  vessels.  Infraorbital  canal  opens 
just  below  the  margin  of  the  orbit.  Malar 
foramina  is  a  passage  for  nerves  and  vessels  from 
the  orbit. 

Angle,  A  figure  formed  by  two  straight  lines  ex- 
tending out  from  one  point  in  different  direc- 
tions. yAngle  Gamma  is  formed  at  the  center  of 


no  LEWIS  POCKET 

rotation  of  the  globe  by  the  optic  axis  and  a  line 
drawn  from  the  point  on  the  object  looked  at. 
Angle  of  Convergence  is  the  angle  which  the  two 
visual  axes  form  in  turning  from  infinity  to  a 
point  less  remote.  The  angle  thus  formed,  when 
the  two  visual  axes  are  directed  to  a  point  one 
meter  distant  on  the  median  line,  is  called  a 
meter  angle  of  convergence,  and  is  the  unit  of  the 
angle  of  convergence.  When  the  visual  axes  meet 
on  the  median  line,  at  a  half  meter  distance,  it 
is  called  a  two-meter  angle  of  convergence,  and 
when  looking  at  a  third  meter  distance  it  is  called 
a  three-meter  angle  of  convergence.  V  Visual  A. 
is  an  angle  formed  by  rays  of  light  coming  from 
the  extremities  of  an  object  looked  at  and  cross- 
ing at  the  nodal  point  of  the  eye.  This  angle 
depends  for  its  existence  upon  the  size  and  dis- 
tance of  the  object.  A.  of  Incidence  is  the  angle 
formed  by  the  incident  ray  with  the  perpendic- 
ular. A.  of  View  (same  as  visual  angle).  Optic 
A.  is  formed  by  the  meeting  of  the  optic  axes  of 
the  two  eyes.  A.  of  Reflection  is  an  angle 
formed  by  the  reflected  ray  with  a  line  per- 
pendicular to  the  reflecting  surface,  and  is  always 
equal  to  the  Angle  of  Incidence. 

s.    Angle  Alpha  (ang'gel  al'-fa).     The  angle  formed  by 
the  optic  and  visual  axis. 

Angle  of  Incidence.     The  angle  formed  by  the  inci- 
dent ray  with  the  perpendicular. 

Angle  of  Refraction.     The  angle  formed  by  the  re- 
fracted ray  with  the  perpendicular. 

Anian'thinopsy.       Inability    to     distinguish    violet 
shades. 


OPTICAL  DICTIONARY.  21 

Aniridia  (an-ir-id'-e-ah).     Congenital  absence  of  the 

iris. 
Anisocoria  (an-is-o-ko'-re-ah).  That  condition  where 

the  two  pupils  are  unequal. 

Anisometropia  (an-is-o-me-tro'-pe-ah).  A  diflfer- 
\.  ence  of  refraction  in  the  two  eyes.  The  defect  is 
usually  congenital,  but  it  can  be  acquired,  as  in 
Aphakia,  or  operations  of  any  kind.  One  eye 
may  be  emmetropic,  the  other  hypermetropic,  or 
myopic,  or  one  more  hypermetropic,  myopic,  or 
astigmatic  than  the  other.  When  one  eye  is 
hypermetropic  or  emmetropic  and  the  other 
myopic,  the  hypermetropic  or  emmetropic  eye 
is  used  for  distance,  and  the  myopic  eye  for  near- 
ness. 

Anisopia  (an-is-o'-pe-ah) .  An  inability  of  both  eyes 
to  receive  equal  impressions,  not  due  to  an  un- 
equal refractive  state. 

Ankyloblepharon  (ang-kil-o-blef'-ar-on).  Adhe- 
sions of  the  edges  of  the  eyelids. 

Annulus  (an'-nu-lus).  A  ring-shaped  organ.  A. 
ciliaris,  boundary  between  iris  and  choroid. 

Anoopsia  (an-o-op'-se-ah) .  Where  the  eye  has 
turned  upward.     (Strabismus.) 

Anophthalmia  (an-off-thal'-me-ah) .  Absence  of  the 
eyes. 

Anopsia  (an-op'-se-ah) .  Disuse  of  the  eye  from 
certain  defects. 

Anortkopia  (an-or-tho'-pe-ah) .  When  the  eyes  are 
turned  from  parallelism.     (Strabismus.) 

Anterior  (front  part).  Referring  to  the  eye,  the 
cornea  would  be  the  most  anterior  point. 


V 


$9  LEWIS  POCKET 

Antimetropia  (an-ti-me-tro'-pe-ah).  Where  one  eye 
is  myopic  and  the  other  hypermetropic. 

Antiseptic  (an-ti-sep'-tik).  A  substance  which  is 
destructive  to  poisonous  germs. 

Apex  (a'-pex).     The  thin  edge  of  a  prism. 

\i  Aphakia  (ah-fa'-ke-ah).  Absence  of  the  crystalline 
lens. 

Apical  (a'-pik-al).     Pertaining  to  the  apex. 

Aplanatic  (ah-plan-at'-ik).  That  condition  where 
there  is  neither  spherical  nor  chromatic  aberration , 
and  the  lines  are  also  straight.     (See  Lens.) 

Aponeurosis  (ap-on-u-ro'-sis) .  The  fibrinous  ex- 
pansion of  a  tendon. 

Apparent  Position.  The  position  apparently  occu- 
pied by  an  object  seen  through  a  refracting  me- 
dium, as  distinguished  from  its  real  position. 

^  Appendages  of  the  Eye  are  the  orbits,  the  eyebrows, 
the  eyelids,  the  conjunctiva,  the  lachrymal  appar- 
atus, the  muscles,  the  aponeurosis,  and  vessels 
and  nerves  of  the  orbit. 

Applanatio-corneae  (ap-lan-a'-she-o-kor'-ne-e).  A 
condition  in  which  the  cornea  becomes  flattened. 

^  Aqueous  Humor  (a'-que-us  hu'-mor).  A  transpar- 
ent, watery  fluid  which  fills  the  anterior  and. 
posterior  chambers,  the  iris  becoming  the  boun- 
dary line  between  the  two  chambers.  If  this 
humor  is  allowed  to  escape  it  will  re-form  again. 
Its  index  of  refraction  is  1.33. 

Aquocapsulitis  (a'-kwo-caps-u-li'-tis).  Serous  inflam- 
mation of  the  iris. 


\ 


OPTICAL  DICTIONARY.  23 

Arc.     Any  part  of  a  curved  line. 

Arcus  senilis  (ar'-kus  sen'-il-es).  White  circle  in 
cornea  near  sclerotic.     Condition  in  aged. 

Area  of  Critical  Definition.  That  portion  of  an 
optical  image  within  which  the  detail  is  clearly 
defined. 

Argamblyopia  (ar-gam-ble-o'-pe-ah).  Amblyopia 
from  non-use  of  eye. 

Argyll-Robertson  Pupil.  A  pupil  that  will  not  re- 
spond to  light,  but  contracts  in  accommodation. 
Can  be  seen  in  locomotor-ataxia. 

Artery.  The  vessel  which  carries  the  purified  blood 
from  the  heart  to  the  different  cells  of  the  body. 
The  ophthalmic  artery  supplies  the  eye  with  blood. 

Artificial  Eye.  A  thin  glass  plate  which  resembles 
the  sclerotic,  cornea  and  iris.  Artificial  eyes  are 
made  in  different  sizes  and  colors,  and  are  always 
fitted  to  match  the  sound  eye.  Before  inserting 
the  artificial  eye  it  should  be  put  into  salt  and 
water  for  a  few  minutes,  then  draw  the  upper 
lid  out  and  down,  and  slip  the  eye  up  under; 
then  draw  the  lower  lid  out  and  down,  and  in 
this  way  allow  the  eye  to  fall  into  position.  As  a 
rule,  an  artificial  eye  will  last  about  a  year,  when 
it  begins  to  lose  its  smoothness  and  a  new  one 
is  required. 

Asep'sis.  Free  from  septic  matter,  or  free  from  in- 
fection. 

Asthenopia  (as-then-o'-pi-ah).  Weak  and  painful 
vision;  subdivided  into  three  kinds:  retinal, 
muscular,  and  accommodative. 

Retinal — where  the  eye  cannot  stand  light  with- 
out pain;    intolerance  of  light;    photophobia.  ^ 


LEWIS  POCKET 


OPTICAL  DICTIONARY.  25 

Muscular — a  condition  of  the  eyes  in  which  the 
muscles  controlling  their  movement  sufiFer  from 
speedy  fatigue,  causing  pain. 

Accommodative — fatigue  of  the  ciliary  muscles 
by  hypermetropia,  presbyopia,  or  overwork  in 
emmetropia. 

Astigmagraph  (as-tig'-ma-graf).  An  instrument 
used  to  demonstrate  the  state  or  condition  of 
astigmatism  of  the  eye. 

Astigmatism  (as-tig'-mat-ism") .  Astigmatism  is  a 
term  applied  to  an  eye  whose  refraction  is  not 
the  same  in  all  its  parts,  and  it  is  subdivided  into 
two  kinds,  regular  and  irregular.  Irregular 
astigmatism  is  where  there  is  a  difference  of  refrac- 
tion in  one  and  the  same  meridian,  and  according 
to  Hartridge  is  sur  divided  into  normal  and  ab- 
normal. Normal  irregular  astigmatism  is  due  in 
a  great  measure  to  irregularities  in  the  refracting 
power  of  the  different  sectors  of  the  lens,  and 
causes  a  luminous  point  to  appear  stellate,  or  star 
shape.     The  abnormal  variety  is  usually  caused 

'  by  ulcers,  conical  cornea,  or  injury  of  the  cornea, 
but  the  same  condition  may  be  congenital.  This 
kind  of  astigmatism  cannot  be  corrected  with 
lenses.  Regular  astigmatism  is  where  we  have 
the  meridians  of  greatest  and  least  curvature  at 
right  angles  to  each  other,  and  are  known  as  the 
principal  meridians.  This  variety  can  be  corrected 
with  cylindrical  lenses.  It  has  five  subdivisions, 
which  merely  serve  to  show  the  location  of  the 
focuses,  which  are  as  follows: 

No.  1.  Compound  Hyperopic  Astigmatism  is 
that  condition  in  which  the  foci  of  the  two  princi- 
pal meridians  are  back  of  the  retina  at  different 


26 


LEWIS  POCKET 


places  when  the  eye  is  at  rest  and  looking  at 
infinity. 


No.  1.     Compound  Hyperopic  Astigmatism. 

No.  2.  Simple  Hyperopic  Astigmatism  is 
that  condition  in  which  parallel  rays  enter  the 
eye,  and  one  of  the  principal   meridians   focuses 


No.  2.     Simple  Hyperopic  Astigmatism. 

on  the  retina,  the  other  behind  the  retina,  when 
the  eye  is  at  rest. 


No,  3,     Compound  Myopic  Astigmatism. 

No.    3.     Compound    Myopic    Astigmatism    is 
that  condition  in  which  the  two  principal  merid- 


OPTICAL  DICTIONARY. 


27 


ians  focus  in  front  of  the  retina  at  different 
places  when  the  eye  is  at  rest  and  looking  at 
infinity. 


No.  4.     Simple  Myopic  Astigmatism, 

No.  4.  Simple  Myopic  Astigmatism  is  that 
condition  in  which  one  of  the  principal  meridians 
focuses  on  the  retina  and  the  other  in  front  with 
the  eye  at  rest  and  looking  at  infinity. 


No.  5.     Mixed  Astigmatism. 

No.  5.  Mixed  Astigmatism  is  that  condition 
in  which  one  of  the  principal  ^meridians  focuses 
in  front  of  the  retina  and  the  other  behind  the 
retina  when  the  eye  is  at  rest  and  looking  at 
infinity.  It  derives  its  name,  mixed  astigmatism, 
from  the  fact  that  one  meridian  is  hyperopic  and 
the  other  myopic. 

Corneal  Astigmatism  is  caused  by  irregu- 
larity of  the  curvature  of  the  cornea. 


\ 


LEWIS  POCKET 

Lenticular  Astigmatism  is  caused  by  an  irreg- 
ularity of  the  curvature  of  the  crystalline  lenis. 

Astigmatism  with  the  Rule  is  where  the  axis 
of  a  minus  cylinder  that  will  correct  the  astigma- 
tism is  nearer  the  180th  meridian  than  the  90th, 
or  the  axis  of  a  plus  cylinder  that  will  correct  the 
astigmatism  is  nearel-  90  than  180;  otherwise,  it 
is  against  the  rule. 

Correcting  cases  of  high  astigmatism  often 
proves  unsatisfactory  at  the  time.  When  the 
image  is  formed  on  the  retina  of  such  an  eye  it  is 
much  blurred  at  one  of  the  principal  meridians, 
and  sometimes  distorted.  However,  the  patient 
accepts  this,  as  his  vision  has  never  been  better. 
So  much  so  that  when  the  correct  lenses  form  a 
distinct  retinal  image,  he  fails  to  recognize  it,  and 
will  sometimes  say  that  the  object  looks  distorted, 
as  the  fibers  of  hie  optic  nerve  are  somewhat 
amblyopic,  and  therefore  different  from  those  of 
other  people.  In  such  cases  the  brain  is  in  the 
habit  of  accepting  vision  from  parts  of  the  retina 
that  are  most  distinct,  and  when  wearing  their 
correction  for  the  first  time,  the  vision  shows  very 
little  improvement,  if  any.  It  is  not  uncommon 
for  cases,  of  say  4-D.,  of  astigmatism  to  see  very 
little  better  with  their  glasses  at  the  tinie  of  fitting, 
but  if  they  are  worn  persistently  the  vision  is 
expected  to  improve  in  a  few  months. 

^.stringent  (as-trin'-jent).  An  agent  that  causes 
contraction  and  arrests  discharges. 

A.syininetry  (ah-sim'-et-re).  When  the  eyes  do  not 
correspond,  or  resemble  each  other  in  appeal  ance, 
they  are  said  to  lack  symmetry. 


OPTICAL  DICTIONARY.  29 

Atrophy.  A  wasting  away  of  a  part  from  a  lack 
of  nutrition. 

Atropine.  A  mydriatic  which  is  used  more  than 
any  other  to  suspend  accommodation  and  dilate 
the  pupil.  Atropine  paralyzes  the  sphincter 
muscle  of  the  iris  and  the  ciliary  muscle,  and 
hence  results  in  dilatation  of  the  pupil,  and  also 
in  inability  to  see  clearly  near  by.  The  dilata- 
tion of  the  pupil  is  a  maximum  one.  If,  in  the 
case  of  a  dilatation  of  the  pupil  caused  by  oculo- 
motor paralysis,  atropine  is  instilled,  the  pupil 
becomes  still  more  dilated.  This  proves  that 
atropine,  besides  producing  paralysis  of  the  con- 
tracting fibers,  causes  also  stimulation  of  the 
dilating  fibers.  The  effect  of  the  atropine  makes 
its  appearance  in  from  ten  to  fifteen  minutes 
after  the  instillation,  and  soon  reaches  its  maxi- 
mum. Commencing  with  the  third  day  it  begins 
to  decrease  again,  but  does  not  disappear  com- 
pletely until  after  the  lapse  of  a  week.  The 
instillation  of  atropine,  therefore,  causes  the 
patient  a  disturbance  of  rather  long  duration, 
and  hence  should  be  employed  only  when  there 
is  good  reason  for  it. 

Atropinism  (at'-ro-pin-ism).  A  condition  produced 
by  the  use  of  atropine. 

At'ropinize.     To  put  under  the  influence  of  atropine. 

Autophthalmoscope  (au-tof-thal'-mo-skope).  An 
ophthalmoscope  planned  in  such  a  way  that  a 
person  can  examine  his  own  eyes. 

Axial.     Of,  or  pertaining  to,  an  axis. 

Axially.     In  the  direction  of   the   axis. 


30  LEWIS  POCKET 

A.xis.  Straight  line  through  a  center,  on  which  the 
body  is  supposed  to  revolve.  The^eye  has  two 
principal  axes,  the  optic  and  visual.  vThe  optic 
axis  is  an  imaginary  line  through  the  center  of  the 
cornea,  through  theoiodal  points  to  the  inner  side 
of  the  macula  lutea.\The  visual  axis  is  a  line 
from  the  center  of  the  macula  lutea,  through 
the  nodal  point  to  the  object  looked  at.  When 
speaking  of  the  axis  of  a  cylinder  we  mean  the 
meridian  '  of  a  cylindrical  lens  having  no  power. 
When  parallel  rays  fall  on  the  spherical  surface  of 
a  lens,  the  ray  which  strikes  the  optical  center 
at  right  angles  will  pass  through  unrefracted, 
and  is  known  as  the  principal  axis. 

Axis  of  Refraction.  The  normal  to  the  surface  of  a 
refracting  medium  at  the  point  of  incidence  of 
a  ray  of  light. 

Axonometer  (ax-o-nom'-e-ter) .  Apparatus  for  rap- 
idly determining  the  axis  of  a  cylindrical  lens. 


xSacillar  Layer  (bas'-il-ar) .  The  layer  of  rods 
and  cones  of  the  retina. 

Barometer.  An  instrument  indicating  the  atmos- 
pheric pressure. 

Basalts  Lamina.  Or  membrane  of  Bruch.  The 
membrane  which  separates  the  choroid  from  the 
pigmentary  layer  of  the  retina. 

Base.     Foundation  or  thick  end  of  a  prism. 

Beer's  Knife.  A  knife  with  a  triangular  blade  for 
corneal  incision. 


OPTICAL  DICTIONARY.  31 

Bi,  Is  employed  to  signify  two  things  in  one;  for 
instance,  bifocal,  biconcave,  biconvex. 

Biconcave.     Concave  on  both  sides. 

Biconvex.     Convex  on  both  sides. 

Bifocal.  Double  focus.  There  are  six  kinds, 
namely : 

No.  1.     Solid  bifocal. 

No.  2.     Split  or  Franklin  bifocal. 

No.  3.     Perfection  bifocal. 

No.  4.     Cemented  bifocal. 

No.  5.     Invisible  bifocal. 

No.  6.     Depressed  bifocal. 

The  solid  bifocal  is  now  out  of  date.  The  split 
or  Franklin  bifocal  must  be  worn  in  rims,  while 
the  depressed,  invisible,  and  cemented  can  be 
mounted  without  rims,  but  cannot  be  worn  near 
intense  heat.  A  bifocal  lens  consists  of  two  parts 
of  two  different  foci.  In  presbyopia,  or  old 
sight,  the  upper  is  the  weaker  for  distance,  the 
lower  being  stronger  for  near  objects.  In  myopia, 
the  upper  should  be  the  stronger  and  the  lower 
the  weaker  glass.  In  this  way  the  patient  has 
good  distant  vision  without  the  extra  strain  on 
the  accommodation. 

Canada  Balsam  is  used  in  cementing  Bifocal 
Lenses  in  the  following  manner:  First  be  sure 
that  the  lenses  are  perfectly  clean.  Then 
squeeze  a  small  drop  of  the  balsam  onto  the  large 
lens,  and  press  the  scale  upon  the  balsam 
until  it  spreads  out  thoroughly  between  the 
glasses,  being  careful  not  to  break  the  lenses. 
Then  place  the  lenses  on  a  piece  of  metal  over 
a  small  flame,  and  heat  them  slowly  until  all 
the  bubbles  disappear,  and  until  the  balsam  is 


32  LEWIS  POCKET 

nearly  hard — just  about  hard  enough  to  take  a 
slight  impression  of  the  finger  nail.  It  is  impos- 
sible for  a  novice  to  accurately  judge  just  how 
much  to  heat  the  lenses,  but  with  practice  it 
becomes  a  simple  matter.  The  success  depends 
largely  on  their  being  heated  just  long  enough. 
If  they  are  not  heated  enough  they  will  slide  out 
of  position,  and  if  they  are  heated  too  much  they 
will  chip  off  very  easily. 

Binocular.  Pertaining  to  both  eyes.  In  vision  it 
refers  to  the  ability  of  both  eyes  to  see  the  same 
point  of  an  object  at  the  same  time. 

Biorbital  Angle.     The  same  as  the  optic  angle. 

Birefractive.     Doubly  refractive. 

Blear-eye.     Marginal  blepharitis. 

Blennorrhea  (blen-or-e'-ah) .  Excessive  mucous 
discharge. 

Blepharadenitis  (blef-ar-ad-en-i'-tis) .  Inflammation 
of  the  meibomian  glands. 

Blepharal   (blef ^-ar-al) .     Pertaining  to  the  eyelids. 

Blepharelosis  (blef-ar-el-o'-sis) .  Ingrowing  eye- 
lashes.    (See  Trichiasis.) 

Blepharism  (blef '-ar-ism) .  Where  there  is  an  in- 
ability on  the  part  of  the  patient  to  refrain  from 
winking.      (Blinking.) 

Blepharitis  (blef-ar-i'-tis) .  Inflammation  of  the 
eyelids.  Ciliaris  b.  That  condition  where  the 
hair  follicles  of  the  eyelids  are  inflamed. 


OPTICAL  DICTIONARY.  33 

Blepharoplegia  (blef-ar-o-ple'-ge-ia).  That  state  in 
which  the  eyelid  is  paralyzed,  causing  ptosis. 

Blepharoptosis  (blef-ar-op-to'-sis).  That  condition 
where  the  upper  eyelid  droops  from  paralysis. 

Blepharospasm  (blef -ar-o-spasm) .  That  condition 
in  which  there  is  a  spasm  of  the  orbicular  muscle 
of  the  eyelids. 

Blepharostat  (blef-ar'-o-stat) .  An  instrument  used 
for  holding  the  eyelids  apart. 

Blepharostenosis  (blef-ar-o-ste-no'-sis) .  A  narrow- 
ing of  the  palpebral  slit  between  the  eyelids. 

Blepharosynechia  (blef-ar-o-sin-ek'-i-a) .  A  condi- 
tion in  which  there  is  a  growing  together  of  the 
eyelids. 

Blepharotomy  (blef-ar-ot'-o-me).  A  surgical  opera- 
tion for  the  cutting  of  the  eyelid. 

Blind.  Loss  of  sight.  Day-blindness  is  where 
vision  is  better  at  night.  Night-blindness  is  de- 
fective vision  at  night-time. 

\'   Blind   Spot.      Also    known    as   the    optic    disc,    or 
'    papilla.     It  is  the  entrance  of  the  optic  nerve 
on  the  retina. 

Blinking.  That  condition  in  which  there  is  slt 
involuntary  winking. 

Bonnet's  Capsule.     The  same  as  Tenon's  Capsule. 

Bowman's  Membrane.  The  second  anterior  layer 
of  the  cornea. 


34  LEWIS  POCKET 

Brachymetropia  (brach-e-me-tro'-pe-a) .  The  same 
as  myopia  and  hypometropia.  It  is  an  eye  where 
parallel  rays  of  light  will  fociis  in  front  of  the 
retina  with  the  muscles  of  accommodation  at  rest. 

Brain.     A  nervous  mass  within  the  skull. 

Buphthalmia  (buf-thal'-meh-ah) .  Enlargement  of 
the  eye. 

Bupiithalmus.     (See  Buphthalmia.) 


\ 


V 


l^yampimeter  (kam-pim'-e-ter) .  An  instrument 
for  measuring  the  field  of  vision. 

Canada  Balsam.  A  product  obtained  from  a  tree 
that  grows  in  Canada,  and  is  used  for  the  purpose 
of  cementing  lenses.  It  is  easily  melted  if  heated, 
and  readily  soluble  in  alcohol. 

Canals  of  Fontana.  A  number  of  little  spaces  or 
openings  between  the  iris  and  cornea,  in  the 
sclerotic.     (See  Anatomy.) 

Canal  of  Petit.  The  space  which  surrounrls  the 
crystalline  lens  between  the  suspensory  ligaments. 

Canal  of  Schlemm.  Circular  canal  surrounding  the 
eye  at  sclerocorneal  junction.     (See  Anatomy.) 

Canal  of  Stilling.  The  canal  which  runs  through 
the  vitreous  humor  from  the  entrance  of  the 
optic  nerve  to  the  posterior  surface  of  the  lens. 
It  is  lined  by  the  hyaloid  membrane.  This  canal 
is  said  to  convey  the  minute  artery  from  the 
central  artery  of  the  retina  to  the  back  of  the 
iens,  during  development  of  the  eye.  The  artery 
then  disappears,  but  the  canal  remains. 


OPTICAL  DICTIONARY.  35 

Canthectomy  (kan-thek'-to-my).  An  operation  in 
which  part  of  the  can  thus  is  cut  away. 

Canthitis  (kan-thi'-tis) .  Inflammation  of  the  angles 
of  the  eyelids. 

Canthoplasty  (kan'-tho-plas-te).  A  surgical  opera- 
tion for  lessening  the  pressure  and  friction  of  the 
upper  lid  by  cutting  the  outer  canthus.  Plastic 
c.  operation,  an  operation  for  restoring  a  lost 
part. 

Canthotomy  (kan-thot'-o-me).  An  operation  for  the 
slitting  of  either  canthus. 


\' 


Can'thus.     The  angle  at  the  junction  of  the  eyelids, 
known  as  the  inner  and  outer  canthi. 


\ 


Capsule  (kap'-sule).  A  sac  which  encloses  an  organ 
for  the  purpose  of  support,  protection,  and  lubri- 
cation. 

Capsule  of  Tenon.     (See  Tenon's  Capsule.) 

Capsulitis  (knp-su-li'-tis).  Inflammation  of  the 
capsule  of  the  crystalline  lens. 

Capsulotomy  (kap-su-lot'-o-my) .  An  operation  for 
the  cutting  of  a  capsule,  as  that  of  the  lens. 

Cardinal  Points.     (See  Nodal  Point.)  * 

Cartilage  (kar-'til-aj).  The  gristle  or  white  elastic 
substance  in  different  parts  of  the  body. 

Caruncula  Lachrymalis  (kar-un'-ku-lah) .  Is  the 
small  reddish  body  at  the  inner  canthus  of  the  eye. 

Cast.  A  cast  in  the  eye  would  apply  to  strabismus, 
or  squint. 


\ 


36  LEWIS  POCKET 

Cataphoria  (kat-af-o'-re-ah) .  A  tending  of  one  eye 
downward.  If  it  is  the  right  eye  it  is  right 
cataphoria,  and  if  it  is  the  left  eye  it  is  left  cat- 
aphoria. Esocatophoria  is  the  tendency  of  the 
visual  line  inward  and  downward.  Exocato- 
phoria  is  the  tendency  of  the  visual  line  outward 
and  downward. 

Cataract  (kat'-ar-akt) .  Any  opacity  of  the  crys- 
talline lens  or  lens  capsule  of  the  eye. i^  Lenticu- 
lar c,  an  opacity  of  the  lens  proper.V  Capsular  c, 

'  an  opacity  of  the  lens  capsuJe.V  Senile  c.,*  an 
opacity  of  the  lens  due  to  age.  v  Traumatic  c,  a 
cataract  due  to  an  injury.  Pyramidal  c,  an 
opacity  in  the  center,  yet  at  the  anterior  pole,  of 
the  lens.  Secondary  c,  a  cataract  appearing 
after  the  extraction  of  the  lens,  caused  by  that 
part  of  the  lens  capsule  still  attached  to  the  hya- 
loid membrane  becoming  opaque.  'Cortical  c, 
that  condition  in  which  the  border  or  outer  layeis 
of  the  lens  are  losing  their  transparency.  Hard  c. 
(see  Senile  c).  Soft  c.,  where  the  lens  is  soft  and 
milky.  Polar  c,  an  opacity  confined  to  the  an- 
terior or  posterior  pole  of  the  lens. 

Catop'trics.     Laws  of  reflection  of  light. 

Catoptric  Test  (kat-op'-trik).  A  test  for  cata- 
ract by  light  reflected  from  the  crystalline  lens. 
In.  this  test  ask  the  patient  to  look  straight  ahead, 
then  hold  a  lighted  candle  about  twelve  inches  in 
front  of  the  eye,  a  little  to  one  side,  while  you 
stand  slightly  on  the  other  and  look  into  his 
pupil.  If  there  is  no  opacity  of  the  lens  or  cap- 
sule you  will  notice  three  images  of  the  candle. 
The  first  will  be  on  the  surface  of  the  cornea  in  an 
upright  position,  the  second  will  be  on  the  an- 


OPTICAL  DICTIONARY.  37  ' 

terior  surface  of  the  lens,  also  upright,  while  the 
tliird  will  be  inverted  and  much  smaller  on  the 
posterior  surface  of  the  lens,  but  when  there  is  a 
cataract  you  will  fail  to  find  the  inverted  image. 

Cat's-eye  Pupil.  Where  the  pupil  of  the  eye  is  long 
and  narrow  (slit-like). 

Center  (of  Curvature).  If  the  surface  of  a  lens  were 
completed  so  as  to  form  a  circle,  its  center  would  be 
the  center  of  curvature.  (For  Optical  Center  see 
appendix).  , 

Centimeter  (sen'-tim-e-ter) .  One-hundredth  part  of 
a  meter. 

Centrad  (sen'-trad).  Toward  the  center;  unit  of 
measurement  for  prisms  which  will  produce  a 
deviation  in  a  ray  of  light  one-hundredth  of  a 
radian. 

Centric  (sen'-trik).      Pertaining  to  a  nerve  center. 

Ceratitis  (ser-at-i'-tis).     The  same  as  kenititis. 

Ceratonosus  (ser-at-on'-o-sus).  Any  disease  of  the 
cornea. 

Ceratotome  (se-rat'-o-tom).  A  knife  for  dividing 
the  cornea. 

V  Chalazion  (chal-a'-zi-on).  A  tumor  on  the  eyelid. 
On  the  under  surface  of  the  tarsal  plate  of  the 
upper  and  lower  lid  are  numerous  creases  or 
depressions  running  at  right  angles  to  the  margin 
of  the  lid.  There  are  about  thirty  of  them  in  the 
upper  lid  and  about  twenty  in  the  lower.  In 
these  depressions  are  small  tubular  glands,  called 
meibomian  glands,  and  their  ducts  open  next  to 


38  LEWIS  POCKET 

the  margin  of  the  lid.  A  chalazion  is  an  enlarge- 
ment of  one  or  more  of  these  glands,  due  to  the 
stoppage  of  their  ducts,  and  is  usually  chronic  in 
character.  A  chalazion  is  also  called  a  tarsal 
tumor,  tarsal  cyst,  or  meibomian  cyst,  etc.  It  is 
not  a  true  retention  cyst,  but  its  contents  may 
soften  so  that  it  will  become  an  encysted  abscess. 
At  first  its  contents  are  gelatinous,  but  later  may 
become  purulent.  The  tumor  is  firm,  round, 
with  the  skin  moving  freely  over  the  mass,  but 
it  is  firmly  attached  to  the  tarsal  plate.  It  has 
so  much  the  appearance  of  a  sebaceous  cyst  that 
one  is  liable  to  be  mistaken  in  the  diagnosis, 
unless  he  is  familiar  with  the  disease.  Usually 
chalazion  tends  toward  the  conjunctiva,  and,  if 
the  lid  is  everted,  the  position  of  the  tumor  may 
be  located  by  a  bluish  discoloration,  or,  if  the 
contents  are  purulent,  a  yellowish  discoloration. 
The  primary  cause  of  this  trouble  is  not  definitely 
known,  but  a  debilitated  condition  of  the  system, 
eye-strain,  and  blepharitis  marginalis  seem  to  be 
the  factors  in  producing  chalazion. 

Chambers.  The  spaces  of  the  eye.  Anterior  c,  the 
space  between  the  cornea  and  the  iris.  Posterior 
c,  the  space  between  the  iris  and  the  lens. 

\/ 

Check  Ligament.     A   few   fibers    attached   by  one 

end  to  the  anterior  wall  of  the  orbit  and  by  the 
other  to  the  tendons  of  the  recti  muscles.  Those 
on  the  inner  side  are  called  the  internal  check 
ligaments,  and  those  on  the  outer  or  temple  side 
the  external  check  ligaments.  The  action  of 
these  ligaments  is  a  normal  one.  They  probably 
prevent  or  retard  over-action  of  the  abductor^ 
or  adductors. 


OPTICAL  DICTIONARY.  39 

Cheniosis  (ke-mo'-sis) .  Edema  of  the  conjunctiva 
of  the  eye. 

Chiasm  (ki'-asm).  A  crossing;  especially  the  cross- 
ing of  the  fibers  of  the  optic  nerve  (optic  com- 
missure) . 

Chiastometer  (ki-as-tom'-e-ter) .  An  instrument  for 
ascertaining  the  deviation  of  the  optic  axis. 

Chlorophaue  (klo'-ro-fan).  A  green-yellow  pigment 
irom  the  retina. 

^  Choked  Disc.     Congested  and  inflamed  state  of  the 
optic  disc. 

Chondral  (kon'-dral).     Pertaining  to  cartilage. 

Choroid  (ko'-roid).  A  part  of  the  second  tunic. 
(See  Tunic.) 

Choroidal  Fissure.  The  opening  in  the  choroid 
through  which  the  optic  nerve  passes  to  form  the 
retina. 

Choroideremla  (ko-roi-de-re'-me-ah).  Absence  of 
the  choroid. 

Choroiditis  (ko-roi-di'-tis).  Inflammation  of  the 
choroid. 

Choroidocycli'tis.  Inflammation  of  the  choroid  and 
ciliary  processes. 

Choroidoiritis  (ko-roi-do-i-ri'-tis).  Inflammation  of 
the  choroid  and  iris. 

Choroidoretini'tis.  Inflammation  of  the  choroid  and 
retina, 


40  LEWIS  POCKET 

Chromatic   (kro-mat'-ik).     Relating  to  color. 

Chromatic  Aberration.     (See  Aberration.) 

Chromatodysopia  (kro-mat-o-dys-o'-pi-ah) .  Color- 
blindness. 

Chromatology  (kro-mat-ol'-o-gy) .  The  study  of 
colors. 

Chromatom'eter.  An  instrument  for  measuring 
color  or  color  perception. 

Chromatophobea  (kro-mat-o-fo'-be-ah).  An  ab- 
normal fear  of  color. 

Chromatopsia  (kro-mat-op'-se-ah) .  Abnormal  sen- 
sation of  color,  due  to  disorders  of  the  optic  cen- 
ters, or  to  drugs,  especially  santonin. 

Chromatoptometry  (kro-mat-op-tom'-et-ry) .  Tak- 
ing the  measurement  of  the  power  of  color  per- 
ception. 

Chromometer  (kro-mom'-et-er) .  An  instrument  for 
measuring  coloring  matter  present. 

Chronioptometer  (kro-mop-tom'-et-er).  An  instru- 
ment to  test  the  color  sense. 

Cibisitome  (sib-is'-it-om) .  An  instrument  for  in- 
cising the  lens  capsule. 

Cilia.     The  eyelashes.     Hair. 

Ciliariscope  (sil-i-arMs-cope).  An  ins^v^xument  for 
examining  the  ciliary  region  of  the  eye. 

Ciliary  (sil'-i-a-ry)  Pertaining  to,  or  like,  the  eye- 
lashes. 


OPTICAL  DICTIONARY.  41 

Ciliary  Body.  The  middle  part  of  the  second  tunic, 
composed  of  ciliary  processes,  ciliary  veins,  ciliary 
muscles,  ciliary  nerves  and  arteries. 

Cillo  (cilMo)  or  Cillosis.  A  trembling  or  spasmodic 
twitch  of  the  eyelids. 

Cinerea  (sin-e'-re-ah).  The  gray  matter  of  the 
nervous  system. 


Cut  showing  Chori^id  Ciliary  Muscle  and  Nerves. 

Circles  of  Haller.  Venous  and  arterial  circles  of  the 
eye. 

Circulation  (cir-cu-la'-shun).  The  passage  of  blood 
in  going  from  and  returning  to  the  heart  after 
having  made  a  circuit  of  the  body. 

\  Clonic   Spasm.     An  intermittent    involuntary  con- 
^  traction  of  the  ciliary  muscles,  which  shows  itself 
when  the  eye  is  in  use. 


*2  LEWIS  POCKET 

Cocain  (ko-ka'-in).  A  local  anesthetic  and  mydri- 
atic. Cocain  dilates  the  pupil,  and  hence  would 
seem  to  call  for  mention  in  this  place,  although, 
strictly  speaking,  it  does  not  belong  to  the  myd- 
riatics proper — that  is,  the  dilatation  of  the  pupil 
by  cocain  is  not  produced,  as  in  their  case,  by 
its  action  upon  the  contracting  or  the  dilating 
fibers  of  the  iris,  but  by  a  contraction  of  the 
blood-vessels  of  the  iris.  The  dilatation  of  the 
pupil  is  therefore  only  a  moderate  one,  and  the 
reaction  of  the  pupil  to  light  persists;  moreover, 
mydriatics  and  miotics  still  produce  an  effect. 
If  cocain  is  instilled  into  an  eye  the  pupil  of 
which  has  been  dilated  by  atropine,  the  dilata- 
tion increases  somewhat  in  consequence  of  the 
anaemia  of  the  iris  which  then  ensues;  hence  the 
mydriasis  produced  by  the  simultaneous  action 
of  atropine  and  cocain  is  the  most  complete 
that  can  possibly  be  attained.  The  accommo- 
dation is  not  paralyzed  by  cocain,  but  only 
somewhat  weakened. 

CoUyrium  (col-lyr'-i-um).  Any  lotion  to  be  dropped 
in  the  eye. 

V  Coloboina  (kol-o-bo'-mah).     A  tear  or  break  in  the 
eyeball,  as  in  the  iris  or  choroid. 

Golor-Blindness  (Achromatopsia).  Bhndness  for  one 
or  more  colors.  Due  to  the  absence  from  the 
retina  of  one  or  two  of  the  three  primary  sub- 
stances (according  to  Hering).  The  test  is  made 
by  presenting  the  patient  with  samples  of  differ- 
ent colored  yarns — a  number  of  each  color,  but 
different  shades — and  the  patient  is  requeste/i  to 
separate  them.  Persons  having  this  anomaly  of 
vision  are  generally  unaware  of  it  themselves. 


OPTICAL  DICTIONARY.  4^ 

Uommissure  (kom'-mis-ur)  (Optic).  The  crossing 
of  the  two  optic  nerves. 

Compound.  A  lens  that  contains  a  sphere  and  a 
cylinder. 

Comus  (ko'-mus).  A  cone.  A  crescentic  patch 
of  atrophic  choroid  tissue  near  the  optic  papilla 
in  myopia. 

Concave.     The  negative  of  convex. 

Concavo-convex.  Concave  on  one  side  and  convex 
on  the  other.  If  the  convexity  exceeds  the  con- 
cavity it  is  known  as  a  periscopic  convex  lens. 
If  the  concavity  exceeds  the  convexity  it  is 
known  as  a  periscopic  concave  lens. 

Concentric.     Having  a  common  center. 

Concomitant  (kon-com'-it-ant) .  Accompanying. 
Concomitant  Squint  is  a  condition  where  the  two 
eyes  deviate,  but  accompany  one  another  in  their 
movement.  The  object  can  be  seen  by  either 
eye,  but  not  the  two  eyes  at  the  same  time. 

Cone  Muscle  Test.  This  consists  of  a  cone  cemented 
to  a  ground  glass  disc,  and  is  used  as  follows:  It 
is  inserted  into  one  cell  of  trial  frame  in  front  of 
the  correction  for  the  ametropia,  which  must  be 
properly  centered  as  to  pupillary  distance,  and  a 
solid  blank  disk  is  put  into  the  cell  in  front  of  the 
other  eye.  The  patient's  attention  is  then  di- 
rected to  a  light  (preferably  a  candle  or  small  gas 
light)  twenty  feet  away;  and  the  action  of  the 
cone  is  such  that  the  light  will  resolve  itself  into 
a  circle  of  light.  The  other  eye  is  then  uncovered, 
and  if  there  is  no  muscular  error  the  light  will  ap- 
pear i^  the  center  of  the  circle.    If  there  is  mus- 


14  LEWIS  POCKET 

cular  srror  the  light  will  be  either  above  or  below 
or  to  one  side  of  center,  and  can  be  brought  to 
.•:enter  by  the  proper  prism  with  base  in  proper 
position.     This  does  away  with  necessity  for  com- 


Cone. 

putations  where  there  is  combined  prismatic  error 
in  different  angles,  and  gives  at  once  the  position 
of  the  base  of  the  correcting  prism.  (See  Muscu- 
lar Imbalance.) 

Conical  Cornea.  A  condition  of  the  cornea  in  which 
it  bulges  forward  in  the  shape  of  a  cone. 

Conjugate   (coupled). 

Conjugate  Foci  (kon'-ju-gat).  Two  points  so  sit- 
uated in  relation  to  each  other  that  the  direction 
of  a  ray  proceeding  from  either  of  them,  after 
reflection  or  refraction,  passes  through  the  other. 
Secondary  C. — A  conjugate  foci  formed  on  a 
secondary  axis. 


OPTICAL  DICTIONARY,  id 

Conjunctiva  (kon-junc-ti'-va).  The  mucous  mem- 
brane lining  the  eyeUds  and  anterior  covering  c>f 
the  cornea,  and  is  supplied  by  a  branch  of  the 
fifth    sensory   nerve    (ophthalmic). 


V 


Conjunctivitis  (kon-junc-tiv-i'-tis).    Inflammation  of 
the  conjunctiva. 


Convergence  (kon-ver'-gence).  The  power  of  turn- 
ing the  two  eyes  to  a  given  point  inside  of  infinity. 
In  the  emmetropic  eyes  of  a  healthy  person,  the 
two  functions  of  accommodation  and  conver- 
gence work  together  so  that  they  can  scarcely  be 
performed  separatel3\  Yet  their  objects  are 
totally  different,  but  their  harmonious  co-opera- 
tion is  none  the  less  essential.  The  function  of 
accommodation  has  for  its  purpose  the  formation 
of  a  clearly  defined  image  on  the  retina  of  each 
eye  singly;  while  the  function  of  convergence  is 
the  fusing  of  the  two  retinal  images  into  a  single 
sensory  perception;  that  is  to  say,  the  turning  of 
the  two  eyes  inward  so  that  the  image  will  fall 
on  corresponding  parts  of  each  retina;  but  an 
object  at  a  given  distance  will  always  require 
from  the  same  pair  of  eyes  the  same  amount  of 
accommodation,  and  it  will  also  require  from 
them  the  same  amount  of  convergence.  Say  the 
object  is  at  thirteen  inches,  where  it  will  require 
three  diopters  of  accommodation,  then  it  will  also 
require  three  meter  angles  of  convergence;  that 
is  to  say,  convergence  to  such  a  degree  that  the 
lines  of  direction  of  the  two  eyes  would  intersect 
at  a  point  thirteen  inches  from  them;  and  further, 
that  if  the  object  was  brought  nearer,  the  accom- 
modation and  convergence  would  increase  to  an 
equal   extent.     When   one's   eyes   accommodate 


46  LEWIS  POCKET 

more  than  they  converge,  in  order  to  see  at  a 
single  point,  they  are  hyperopic  to  the  extent 
of  the  difference  between  the  two  functions; 
and  when  they  converge  more  than  they  accom- 
modate for  a  given  point,  they  are  myopic  the 
difference.  This  of  course  refers  to  errors  of 
refraction. 

Convergent,     Turning  toward  the  same  point. 

Convex.  That  which  has  a  rounded  and  elevated 
surface.  The  surface,  if  continued  at  the  same 
radius  of  curvature,  would  form  a  complete 
circle,  or  sphere. 

Convexo-concave,  Convex  on  one  side  and  con- 
cave on  the  other.  If  the  convexity  exceeds  the 
concavity  it  is  known  as  a  periscopic  convex 
lens.  If  the  concavity  exceeds  the  convexity  it 
is  known  as  a  periscopic  concave  lens. 

Copiopia  (kop-i-o'-pi-ah) .  A  worn-out  state  of  the 
eye,  caused  by  eye  strain. 

Coreclisis  (kor-ek'-lis-is).  That  condition  in  which 
the  pupil  of  the  eye  is  obliterated. 

Corectasis  (kor-ek'-tas-is.)     Dilatation  of  the  pupil. 

Corectome  (kor-ec'-to-me).  An  instrument  used  in 
cutting  for  iridectomy. 

Corectopia  (kor-ec-to'-pi-ah).  That  condition  in 
which  the  pupil  is  displaced. 

Coredialysis  (kor-e-di-al'-ys-is).  An  operation  in 
which  the  iris  is  detached  from  the  ciliary  liga- 
ment for  a  new  pupil. 

Corelysis  (kor-el'-ys-is) .  Detachment  of  adhesions 
of  the  iris  to  the  cornea  or  the  lens  capsule. 


OPTICAL  DICTIONARY.  47 

Coremorphosis  (kor-e-mor'-pho-sis) .    Creation  of  an 

artificial  pupil. 
Coreometer    (kor-e-om'-et-er) .     A  contrivance  used 

for  measuring  the  pupil. 

Cornea  (kor'-ne-ah) .  The  anterior  and  transparent 
V  part  of  the  eyeball.  It  has  no  blood-vessels,  but 
plenty  of  nerves  and  lymphatics.  It  serves  to 
transmit  light  into  the  eye.  It  is  convex  in  front 
and  concave  behind.  Its  curvature  varies  in 
different  individuals.  It  is  composed  of  five 
layers,  arranged  as  follows,  from  without  inward: 
namely,  (1)  Conjunctiva  epithelium;  (2)  Bow- 
man's Membrane;  (3)  Cornea  proper;  (4)  Mem- 
brane Descemet;  (5)  Endothelium.  The  third 
layer  (cornea  proper)  is  the  foundation  layer  of 
the  cornea.  It  is  composed  of  a  horn-like  sub- 
stance and  is  non-sensitive  and  merely  serves  to 
keep  the  cornea  in  shape.  Th(^  second  layer 
(Bowman's  Membrane)  is  a  layer  of  sensitive 
nerves  and  elastic  tissue,  and  protects  the  cornea 
proper  on  the  anterior  side,  and  at  the  same  time 
gives  the  cornea  an  elastic  nature.  The  first  layer 
(Conjunctiva  epithelium)  serves  to  protect  the 
nerves  in  Bowman's  Membrane  from  cold,  wind, 
and  dust,  and  at  the  same  time  gives  a  highly 
polished  surface  to  the  cornea.  The  fourth  layer 
(Membrane  Descemet)  is  a  layer  similar  to  Bow- 
man's Membrane,  and  protects  the  cornea  proper 
from  any  diseased  condition  from  the  posterior 
side.  The  fifth  layer  (Endothelium)  is  a  lining 
membrane  which  separates  the  aqueous  humor 
from  the  fourth  layer,  and  at  the  same  time  forms 
a  sort  of  sac  which  contains  the  aqueous  humor. 
The  cornea  has  an  index  of  refraction  of  1.33. 
Its  nerve  supply  arises  from  the  ciliary  nerves. 


48  LEWIS  POCKET 

Cor'neal.     Pertaining  to  the  cornea. 

Corneal  Astigmatism.     (See  Astigmatism.) 

Corneal  Facets  (fas'ets).  Small,  plain  distinct  sur- 
faces  of  the  cornea. 

Corneitis  (cor-ne-i'-tis).,    Inflammation  of  the  cornea. 

Corneo-iritis.     Inflammation  of  the  iris  and  cornea. 

Correction.  Making  good  an  abnormal  condition, 
such  as  correcting  an  error  of  refraction. 

Cortical  (kor'-tik-al) .  To  be  near  the  border. 
Cortical  cataract  is  that  variety  in  which  the 
opacity  begins  at  the  border  of  the  crystalline 
lens  and  gradually  spreads  toward  the  center, 
which  it  sooner  or  later  involves. 

Couching.  That  condition  in  which  the  lens  is  dis- 
placed in  cataract.  This  operation  is  now  obso- 
lete. 

Cover  Test.  A  test  for  muscular  imbalance  by 
covering  one  eye  and  observing  its  movement 
while  uncovering;  the  point  of  fixation  being 
established. 

Cramp.     A  spasmodic  muscular  contraction. 

Cribriform  (krib'-rif-orm).      Perforated  like  a  sieve. 

Critical  Angle  (krit'-ik-al) .  The  least  angle  of 
incidence  at  which  a  ray  of  light  traveling  in  a 
denser  medium  is  totally  reflected  at  the  surface 
which  separates  it  from  a  rarer  medium;  also 
known  as  limit  angle. 

Crossed  Diplopia.     (See  Diplopia.) 


OPTICAL  DICTIONARY. 


411 


Crystalline  Lens  (krys'-tal-een) .  The  lens  of  the 
eye  which  resembles  a  crystal,  located  behind  the 
iris,  and  is  made  up  of  layers  like  an  onion,  which 
give  it  an  elastic  nature.  The  lens  itself  is  en- 
closed in  the  lens  capsule,  which  is  held  in  its  posi- 
tion by  the  suspensory  ligaments.  Its  index  of 
refraction  is  1.43.  The  lens  of  the  eye  repre- 
sents from  19  to  20D.  of  plus  when  at  rest. 

Crytometer.     (See  Curtometer.) 


Cupped  Disc, 

\  Cupped  Disc.     That  condition  in  which  the  optic 
disc  has  become  cupped,  as  seen  in  glaucoma. 

Curtom'eter.     An  instrument  for  measuring  curved 
surfaces. 


Curvature    (curv'-r.-ture) .     The  bending   of   a  line 
withoat  forming  angles. 


50  LEWIS  POCKET 

Cyclitis  (cyc-li'-tis).  Inflammation  of  the  ciliary 
body. 

Cyclochoroidi'tis.  Inflammation  of  the  choroid  and 
ciHary  body. 

Cyclophoria  (cyc-lo-fo'-ri-ah).  That  condition  in 
which  the  vertical  axis  of  the  eye  inclines  to  the 
right  or  left  instead  of  standing  vertically,  the  ex- 
trinsic muscles  being  at  rest. 

Cyclopia  (si-klo'-pe-ah) .  A  single  eye  in  center 
of    forehead. 

Cycloplegia  (cy-clo-ple'-gi-ah).  Paralysis  of  the 
ciliary  muscles. 

Cycloplegic.  A  drug  which  produces  para/ysis  of 
the  ciliary  muscles,  or  muscles  of  accommodation. 

Cylinder  (cylMn-der).     (See  Lens.) 

Cystitome  (sis'-tit-om).  An  instrument  used  for 
opening  the  sac  of  the  crystalline  lens. 


JLl»     Abbreviation    for    diopter,  dexter,  or  dose. 

Dacryadenalgia  (dak-ry-ad-en-ar-gi-ah) .     Pain  in  a 
lacrimal  gland. 

Dacryagogue    (dak'-ry-ag-og).     A    medicine    which 
causes  a  flow  of  tears. 

Dacryoadenitis    (dak-ry-o-ad-en-i'-tis) .      Inflamma- 
tion of  a  lacrimal  gland. 

Dacryocele  (dak'-ry-o-cele) .    A  cyst  of  the  lacrimal 
sac. 


OPTICAL  DICTIONARY.  61 

k)acryocyst  (dak'-ry-o-cyst) .     The  tear  sac. 

Dacryocystalgia  (dak-ry-o-cyst-al'-gi-ah).  Pain  in 
the  lacrimal  sac. 

.  Dacryocystitis  (dak-ry-o-cys-ti'-tis).     Inflammation 
V    of  the  lacrimal  sac. 

Dacryoma  (dak-ry-o'-ma).  A  lacrimal  tumor 
which  causes  an  obstruction  of  the  lacrimal 
puncta,  so  that  the  tears  flow  over  the  lids 
upon  the  cheek. 

Dacryon  (dak'-re-on).  The  lacrimal  point;  a  place 
where  the  lacrimal,  frontal,  and  upper  maxillary 
bones  meet. 

Dacryops  (dak'-re-ops) .  That  condition  in  which 
there  is  distention  of  a  lacrimal  duct. 

Dacryorrhea.     Excessive  or  morbid  flow  of  tears. 

Daltonism  (dawr-ton-izm).     Color-blindness. 

Day-blindness  (day-blind'-ness) .  Partially  blind  by 
day,  with  better  vision  at  night. 

Decameter  (dek'-a-me-ter) .     Ten  meters. 

Decentered  (de-cen'-terd)  Lens.  A  lens  -  with  its 
optical  center  to  one  side  or  above  or  below  the 
center. 


Decentered  Lenses. 


Decentering  of  Lenses.  Instead  of  having  a  prism 
and  a  lens  combined  where  you  wish  to  obtain  the 
effect  of  both,  it  is  possible  to  get  the  same  result 
by  simply  decentering  the  optical  center  of  the 


52  LEWIS  POCKET 

lens.  The  optical  center  of  a  plus  lens  is  at  its 
thickest  part,  and  in  the  minus  at  its  thinnest 
part,  while  the  geometrical  center  of  a  lens  is  the 
point  midway  between  all  edges.  A  1-diopter 
lens  decentered  9.4  millimetres  will  give  the 
effect  of  a  1-degree  prism,  while  a  2-D.  lens  will 
only  require  to  be  decentered  half  this  amount, 
or  4.7  millimetres;  a  3-D.  lens,  one-third  of  this 
amount,  or  3. 1  +  mm.  for  the  same  effect,  and 
so  on  according  to  the  strength  of  the  lens.  To 
obtain  the  effect  of  a  2-degree  prism  these  lenses 
'  must  be  decentered  twice  as  much,  that  is  to  saj^, 
a  1-D.  lens,  18.8  mm.;  a  2-D.  lens,  9.4  mm.;  a 
3-D.,  6.3  mm.  From  this  table  one  can  easily 
figure  the  exact  amount  any  lens  should  be  de- 
centered  to  obtain  a  given  prismatic  effect. 

Decentration  (de-cen-tra'-tion).     The  act  of  remov- 
ing from  a  center. 

Decimeter  (des'-im-e-ter) .     One-tenth  of  a  meter- 
Defect   (de-fectO.     A  departure  from  the  normal. 
When  speaking  of  defects  of  vision  we  mean  the 
visual  power  of  the  eye  is  not  normal. 

Defining  Power,  Definition.     The  power  of  a  lens  to 
give  a  clear  outline. 

Depilation    (dep-il-a'-shun).     The   removal   or    loss 
of  the  hair. 

Deplumation  (de-plu-ma'-shun) .     Loss  of  eyelashes 
by  disease. 

Deprimens  Oculi  (dep'-ri-mens  ok'-u-li).    The  rectus 
inferior  muscle. 


OPTICAL  DICTIONARY.  53 

Descemet^s   Membrane    (des-ce-mets'   mem'-brane) 
The  fourth  layer  of  the  cornea.     (See  Cornea.) 

Descemetitis  (des-em-e-ti'-tis) .  Inflammation  of 
Descemet's  Membrane. 

Deviation  (de-vi-a'-shun) .  Turning  aside,  as  in  stra- 
bismus. Conjugate  d.,  deviation  of  both  eyes  to 
the  same  side.  Minimum  d.,  the  smallest  devia- 
tion of  a  ray  that  a  given  prism  can  produce. 

Dexter,  Dextra  (dex'-ter,  dex'-tra).     On  right  side. 

Dextrad  (dex'-trad).     Toward  the  right  side. 

Diameter  (di-am'-e-ter) .  A  straight  line  joining 
opposite  points  of  a  circle. 

Diaphaneity  (di-af-a-ne'-i-ty) .  Transparency;  the 
power  of  transmitting  light. 

Diaphanous  (di-af '-a-nous) .  Having  power  to 
transmit  rays  of  light,  as  glass. 

Diaphragm  (di'-af-ram) .  A  term  applied  to  the 
partition  with  a  central  aperture  in  optical  in- 
struments so  that  rays  of  light  may  be  controlled. 
The  iris  with  its  pupil  constitutes  the  diaphragm 
of  the  eye. 

Diapyesis  (di-ap-i-e'-sis).     Suppuration. 

Diffraction  (dif-f rak'-shun) .  Deflection  or  decom- 
position of  light  in  passing  by  the  edges  of  opaque 
bodies  or  through  small  apertures. 

Diffusion  (dif-f u'-shun) .  A  spreading  or  scattering 
of  rays  of  light,  causing  a  blurred  image  by  im- 
perfect refraction. 

Dilatant.     A  medicine  that  causes  dilatation. 


54  LEWIS  POCKET 

Dilatation  (di-la-ta'-shun).  The  expansion  of  any 
orifice  or  canal. 

Dilator  (di-la'-tor).  Dilator  iris  refers  to  th«  radi- 
ating fiber  of  the  iris  which  dilates  the  pupil. 

Diopter  (di-op'-ter) .  A  lens  of  one  meter  focus  is 
taken  as  the  unit  frorh  the  metric  system,  and  is 
called  a  diopter.  A  lens  of  two  diopters  is  twice 
the  strength  of  the  former,  and  has  a  focal  length 
of  half  a  meter.  Synonyms,  Dioptre  and 
Dioptry. 

Dloptometer  (di-op-tom'-e-ter).  An  instrument  for 
testing  ocular  refraction. 

Dioptometry  (di-op-tom'-e-tre) .  The  measurement 
of  ocular  accommodation  and  refraction. 

Dioptral  (di-op'-tral).     Pertaining  to  a  diopter. 

Dioptrics  (di-op'-triks).  Pertaining  to  refracted 
light. 

Dioptry  (di-op'-tre).     (See  Diopter.) 

Diplocorla  (dip-lo-ko'-re-ah) .     Double  pupil. 

\  Diplopia  (dip-lo'-pe-ah).  Double  vision.  The  ob- 
ject of  convergence  is  to  direct  the  yellow  spot  (or 
macula  lutea)  in  each  eye  toward  the  same  point, 
so  as  to  obtain  single  vision;  diplopia,  or  double 
vision,  at  once  resulting  when  the  image  of  an 
object  falls  on  parts  of  the  retina  ^ich  do  not 
exactly  correspond  in  the  two  eyes.  V  Heterony- 
mous d.,  where  the  object  seen  with  the  right 
eye  appears  on  the  left  side,  and  that  of  the  left 
eye  on  the  right  side.^  Homonymous  d.,  where 
the  object  of  the  right  eye  appears  on  the  right 
side,  and  the  object  of  the  left  eye  on  the  left 
side.     Monocular  d.,  diplopia  with   a   single  eye. 


V 


OPTICAL  DICTIONARY.  65 

Diplopiometer  (dip-lo-pi-om'-e-ter) .  An  instrument 
for  measuring  diplopia. 

Disc  (disk).  A  round  body  which  resembles  a  small 
circular  plate.  Optic  d.,  a  whitish  circular  spot  in 
the  retina  representing  the  entrance  of  the  optic 
nerve  into  the  globe  of  the  eye. 

Discission  (dis-ish'-un) .  The  rupture  of  the  capsule 
of  the  crystalline  lens  in  the  operation  for  soft 
cataract. 

Diseases  of  the  Eye.     The  diseases  of  the  eye  are 

many,  but  nearly  all  of  them  can  be  directly  or 
indirectly  attributed  to  eye  strain  or  impurity  of 
the  blood.  First,  relieve  any  -  eye  strain  by 
glasses.  Second,  keep  the  bowels  regular.  Third, 
fresh  air  and  exercise.  When  the  patient  re- 
quires further  attention,  proper  treatment  should 
be  instituted. 

Disparate  Points  (dis'-par-at) .  Points  on  the 
two  retinae  upon  which  light  does  not  produce  the 
same  impression. 

Dispersing  Lens  (dis-per'-sing).  Same  as  •  con- 
cave lens. 

Dispersion  (dis-per'-shun).  The  process  of  scatter- 
ing the  rays  of  light  through  any  kind  of  a  lens. 

Distichiasis,  Distichia  (dis-te-ki'-a-sis,  dis-tik'-e-ah) . 
That  condition  of  the  eyelashes  in  which  a  second 
row  rubs  against  the  cornea,  causing  inflammation. 

Divergence  (di-ver'-gens) .  To  turn  outward  froOl 
parallelism. 


56  LEWIS  POCKET 

Donders  (Frans  Cornelia).  A  Dutch  physician,  born 
t  Tilburg,  Holland,  May  27,  1818.  He  was 
educated  at  Utrecht,  where  he  became  a  profes- 
sor of  physiology,  histology,  and  ophthalmology 
in  1847.  Among  his  works  are,  **A  Study  of 
the  Movements  of  the  Eyes,"  "Astigmatism,'' 
"Anomalies  of  Refraction  and  Accommodation.'* 
He  died  March  27,  1889. 


Double  Prism. 

Double  Prism.  An  opaque  disc  with  a  slit-like 
opening.  Over  this  slit  there  are  two  prisms 
with  their  bases  together.  Used  for  testing  for 
muscular  imbalance. 

Double  Vision.  Seeing  two  images  instead  of  one. 
(See  Diplopia.) 

Doublet  (doubMet).     Composed  of  two  lenses. 
V  pynamic  Refraction   (dy-nam'-ic).     The  refraction 
of  the  eye  when  adjusted  for  the  near  point.     The 
differenf'e  between  the  dynamic  and  static  refrac- 
tion is  known  as  the  Amplitude  of  Accommodation 


\. 


OPTICAL  DICTIONARY.  57 

-Kccentric    (ek-sen'-trik)       Away  from    a    center. 

Ecchyraosis.     An  extravasation  of  blood  into  tissue. 

Ectasia     (ek-ta'-se-ah) .     Abnormal     distention     or 
dilatation  of  a  part. 

E^tiris  (ek-ti'-ris) .     The  external  portion  of  the  iris. 

Ectochoroidea    (ek-to-cho-roi'-de-ah).      The    outer 
layer  of  the  choroid  coat. 

Ectocornea  (ek-to-kor'-ne-ah) .     Outer  layer  of  the 
cornea. 

Ectoretina   (ek-to-ret'-in-ah) .     Outermost   layer   of 
the  retina. 


Ectropion  (ek-tro'-pi-on)   Ectropium.     Turning  out 
or  inside  out  of  the  edge  of  an  eyelid. 

Em'bolism.    Obstruction  of  a  vessel  by  an  embolus. 

Em'bolus.     A  clot  or  plug  which  obstructs  a  blood- 
vessel. 

Emergent.      A  ray  of    light    after    having    passed 
through  a  refracting  medium. 

Emissive.     Radiating. 


An  emmetropic  eye  receiving  one  set  of  parallel  rays. 
It  must  be  remembered  that  the  three  rays  representing 
the  set  come  from  one  point,  but  the  point  is  so  far  aw^y 
that  the  rays  appear  to  be  parallel  because  the  divergence 
is  so  slight. 


58  LEWIS  POCKET 

Emmetropia  (em-met-ro'-pi-ah) .  An  eye  where 
parallel  rays  of  light  will  focus  on  the  retina  with 
the  muscles  of  accommodation  at  rest.  (Cut, 
p.  57.) 

Encan^this.  A  minute  tumor  in  the  inner  canthus 
of  the  eye. 

Enophthalmus  (en-of-thal'-mus).  A  condition 
where  the  eyes  are  deep-seated. 

Enstrophe  (en'-stro-fe).     A  turning  inward. 

En'tad.     Toward  a  center. 

Entochoroidea  (en-to-cho-roi'-de-ah) .  The  inner 
layer  of  the  choroid. 

Entocornea  (en-to-cor'-ne-ah).  Descemet's  Mem- 
brane. 

Entoptic  (en-top'-tic) .     Situated  within  the  eye. 

Entoptoscppy  (en-top-tos'-co-py) .  Inspection  qf  the 
interior  of  the  eye. 

Entoretina  (en-to-ret'-in-ah) .  The  nervous  or  inner 
layer  of  the  retina. 

Entropion.     (See  Entropium.) 

\'  Entropium  (en-tro'-pi-um) .     A  turning  in  or  inver- 
sion of  the  eyelid  or  eyelashes. 

Enucleate  (e-nu'-cle-ate) .    To  remove  from  its  cover. 

Enucleation  (e-nu'-cle-a'-shun) .  jOperation  for  the 
removal  of  the  eye. 

Epicanthus  (ep-i-can'-thus) .  A  fold  of  skin  pro- 
jected over  the  inner  canthus. 


OPTICAL  DICTIONARY.  59 

Epipbora  (e-pif '-or-a) .     An  overflow  of  tears,  caus- 
ing them  to  run  down  the  cheek. 

Episcleral  Cep-i-scie'-ral)-      Situated  over  the  sclera 
ot  the  eye. 

Episcleritis  (ep-i-scle-ri'-tis) .     Inflammation  of  the 
outer  layers  of  the  sclera. 

Equiribrating  operation.     Tenotomy  of  the  muscle, 
which  antagonizes  a  paralyzed  muscle  of  the  eye. 

Errors    of    Refraction.     Abnormal     conditions    of 
refraction  in  the  eye. 

Erythropsia  (er-ith-rop'-se-ah) .     Red  vision. 

\  Eserine  (es'-er-een) .  An  alkaloid  obtained  from  the 
\r  calabar-bean,  which  will  cause  contraction  of  the 
pupil.  It  has  an  action  exactly  opposite 
to  that  of  atropine,  since  it  places  the  iris  and 
ciliary  muscle  in  a  state  of  tonic  contraction. 
Consequently,  miosis  develops  so  that  the  pupil 
is  about  the  size  of  a  pin's  head,  with  adjustment 
of  the  eye  for  the  near  point,  as  if  marked  myopia 
were  present.  We  generally  apply  sulphate  of 
eserine  in  one  per  cent  solution.  This  solution, 
when  freshly  prepared,  is  colorless,  but  after  some 
days  becomes  red,  although  without  losing  its 
activity.  The  instillation  of  eserine  produces, 
simultaneously  with  the  changes  in  the  iris,  a 
feeling  of  great  tension  in  the  eye,  and  frequently 
headache  and  even  nausea,  so  that  with  many 
persons  it  cannot  be  employed.  For  this  reason, 
hydrochloride  of  pilocarpine,  prescribed  in  a  one 
to  two  per  cent  solution,  is  recommended  as  a 
miotic    for    ordinary    use.     Its    solution    keeps 


60  LEWIS  POCKET 

better  than  that  of  eserine,  and  does  not  act  as 
powerfully  as  the  latter,  but  is  not  accompanied 
by  any  unpleasant  complications.  Eserine  is 
best  reserved  for  those  cases  in  which  pilocarpine 
is  ineffectual. 

\^  Esophoria  (es-o-f o'-ri-ah) .     A  tendency  of  the  eyes 
to  deviate  inward,  usually  caused  by  hyperopia. 

Esotropia    (e-so-tro'-pi-ah) .     This  term  expresses   a. 

^       stronger  meaning  than  Esophoria,  in  which  there 

is  merely  a  tendency,  while  in  Esotropia  there  is 

a   positive   and   visible   appearance    of   the   eyes 

turning  inward. 


V 


Excavation  (ex-cav-a'-shun).  Excavation  of  optic 
nerve;  cupping  or  hollowing  of  the  optic  disc. 

Exophoria  (ex-o-f o'-ri-ah) .  A  tendency  of  the  eye 
to  deviate  outward. 

Exophthalmic  Goiter  (eks-off-thal'-mik  goi'ter).  A 
goiter  with  exophthalmos  and  cardiac  palpitation; 
Basedow's  disease;  Graves'  disease.  The  most 
prominent  symptoms  are  protrusion  of  the  eye, 
excited  action  of  the  heart,  enlarged  thyroid 
(goiter),  and  certain  nervous  phenomena.  The 
protrusion  is  almost  invariably  bilateral,  though 
not  infrequently  greater  on  the  right  side.  The 
upper  lids  do  not  follow  the  eyeball  in  looking 
down  (Von  Graefe's  sign);  infrequency  of  involun- 
tary winking  (Stellwag's  sign)  and  abnormal 
width  of  the  palpebral  aperture  are  also  found. 

Exophthalmos     (ex-of-thal'-mos).     Abnormal     prr 
trusion  of  the  eye. 

Exor'bitism.     Protrusion  of  the  eyeball. 


OPTICAL  DICTIONARY. 


61 


Exotropia  (ex-o-tro'-pi-ah) .     When  the  eye  is  turned 
outward  from  parallelism.     Divergent  strabismus. 

Extraction  (ex-trak'-shun).     The  remrival  of  a  body 
by  surgical  means. 


Eye. 

i<3ye.  The  organ  of  sight.  The  function  of  each 
eye,  taken  singly,  is  to  form  upon  the  retina,  or 
nervous  membrane  which  lines  the  inside  and 
back  part  of  the  organ,  a  sharply  defined  inverted 
image  of  any  object  looked  at.  The  eye  resembles 
a  photographer's  camera,  inasmuch  as  the  image 
produced  upon  the  retina  is  precisely  the  same  as 
that  produced  on  the  ground  glass  of  a  camera. 
By  means  of  the  optic  nerve  the  image  that  is 
received  on  the  retina  is  conveyed  to  the  brain, 


62  LEWIS  POCKET 

which  recognizes  the  visual  appearances  and  com- 
pletes the  act  of  seeing.  More  than  this  we 
do  not  know,  but  we  do  know  that  it  depends 
upon  the  sharpness  and  clearness  of  the  retinal 
image.  If  the  image  is  blurred  and  indistinct  it 
will  be  impossible  for  the  brain  to  recognize  the 
object  accurately. 

Eyebrows.  They  are  two  projecting  arches  of  in- 
tegument covered  with  short  thick  hairs,  which 
form  the  upper  boundaries  of  the  orbits. 

Eyelashes.     The  hair  of  the  eyelids. 

Eyelids.  The  anterior  covering  of  the  eye;  that  por- 
tion of  movable  skin  with  which  the  eyeball  is 
covered  or  uncovered  at  will,  protecting  it  from 
injury  by  their  closure.  The  upper  lid  is  the 
larger,  the  more  movable  of  the  two,  and  is  sup- 
plied by  a  separate  muscle,  levator  palpebrae 
superioris.  When  the  eyelids  are  open  an  ellip- 
tical space  is  left  between  their  margins,  the 
extremities  of  which  correspond  to  the  junction  of 
the  upper  and  lower  lids,  and  are  called  canthi. 
The  outer  canthus  is  more  acute  than  the  inner, 
and  the  lids  here  lie  in  close  contact  with  the 
globe,  but  the  inner  canthus  is  prolonged  for  a 
short  distance  inward,  toward  the  nose,  and 
the  two  lids  are  separated  by  a  triangular  space, 
the  lacus  lachrymaliSo  At  the  commencement 
of  the  lacus  lachrymalis  and  on  the  margin  of 
each  eyelid  is  a  small  conical  elevation,  the 
lachrymal  papilla  (the  puncta),  the  apex  of 
which  is  pierced  by  a  small  orifice,  the  com- 
mencement of  the  lachrymal  canal.  Structures 
of   the   Eyelids.      The   eyelids   are   composed    of 


Posterior  View   of  Eyelid   showing  how 
the  Tears  enter  the  Conjunctiva. 

1.  Orbicularis  Palpebrarum  Muscle. 

2.  Opening  between  the   lids    (Palpebral 

Fissure). 

3.  Lachrymal    Glands,    where    the    tears 

have  their  origin. 

4.  Its  ducts  opening  in  the  fold   of  the 

Conjunctiva. 

5.  Conjunctiva  lining  inside  of  lid. 

6.  Puncta  Lacrimalia,   through  which  the 

tears  pass. 

7.  Inner  Canthus. 


Posterior  View  of  the  Palpebral  (eyelid) 
with  the  Conjunctiva  Removed. 

1.  Origin  of  the  Tensor-tarsi  Muscle. 

2.  Superior  Oblique  Muscle  after  passing 

through  its  Trochlea. 

3.  Inferior  Oblique  Muscle. 

4.  Attachment  of  Orbicularis  Palpebrarum 

on  Nasal  side. 

5.  Tarsal  Cartilages   showing    position    of 

Meibomian  Glands. 

6.  Opening  between  the  lids  known  as  the 

Palpebral  Fissure. 

7.  Lower  part  of  Orbicularis  Palpebrarum 

Muscle. 

8.  The  insertion  of  the  Tensor- tarsi  Muscle 

near  the  Puncta. 

9.  Lachrymal  Sac  in  the  nose. 


OPTICAL  DICTIONARY.  63 

the  following  structures,  taken  in  their  order 
from  without  inward:  Integument,  areolar 
tissue,  fibers  of  the  orbicularis  muscle,  tarsal 
cartilage,  fibrous  membrane,  meibomian  glands, 
and  conjunctiva.  The  upper  lid  has,  in  addition, 
the  aponeurosis  of  the  levator  palpebrae.  The 
integument  is  extremely  thin,  and  continuous  at 
the  margin  of  the  Hds  with  the  conjunctiva.  The 
Subcutaneous  Areolar  Tissue  is  very  lax  and  deli- 
cate, seldom  cor* tains  any  fat,  and  is  extremely 
liable  to  serous  infiltration. 

Eyepiece.  The  lens  or  combination  of  lenses  at  the 
eye  end  of  a  telescope  or  other  optical  instrument 
through  which  the  image  formed  by  the  object 
glass  is  viewed. 

Eyesight.  The  sense  of  seeing;  sight  of  the  eye; 
viewing;    observation. 


i^  acultative  (f ak'-ul-ta-tiv) .     The  power  or  ability 
to  maintain  extra  effort  whenever  called  upon. 

VFalse  Myopia.  Due  to  a  spasm  of  accommoda^ 
tion,  where  the  crystalline,  lens  is  kept  con  vexed 
by  the  spasm  and  simulates  true  myopia. 

\  Far  Point.  The  far  point  or  punctum  remotum  is 
y  the  distant  point  at  which  an  object  may  be  seen 
clearly,  with  the  muscles  of  accommodation  at 
rest.  Properly  speaking,  the  far  point  is  an 
optical  and  not  a  visual  point,  and  is  that  point 
from  which  rays  of  light  will  focus  on  the  retina, 
the  eye  being  in  a  state  of  rest. 


64  LEWIS  POCKET 

Field  of  Vision,  The  area  or  space  which  the  fixed 
eye  can  see. 

Filtration  Angle.     (See  Iritic  Angle.) 

Fissure  (fis'-yur).  A  narrow  cleft  or  depression. 
Palpebral  Fissure,  A  slit  or  opening  between  the 
eyelids. 

Flap  Extraction.  Removal  of  cataract  by  making 
a  flap  in  the  cornea. 

Floating  Specks.  Small  floating  opacities  in  the 
humors  of  the  eye.   (See  Muscae  Volitantes.) 

Focal  (fo'-kal).  Pertaining  to  a  focus.  F.  Depth, 
penetrating  power  of  a  lens.  F.  Distance, 
distance  between  the  center  of  lens  and  its 
principal  focus. 

Focal  Length  of  Lenses. 


opters. 

•  English  Inches. 

Centimeters, 

.12 

320  

800 

.25 

160 

400 

.37 

108  

300 

.50 

80  

200 

62 

60  

170 

.75 

52  

130 

.81 

48  

115 

1.00 

40  

100 

1.12 

36  

90 

1.25 

32  ....... 

80 

1.50 

..  26  

65 

1.75 

22  

55 

2.00 

20  

50 

2.25 

18  

43 

2.50 

16  

40 

2.62 

15  

38 

2.75 

14  .. 

35 

OPTICAL  DICTIONARY.  66 

Focal  Length  of  Lenses — Continued. 

Diopters.  English  Inches.         Centimeters. 

3.00 13     33 

3.25 12     .. 30 

3.50 11 28 

4.00 10     25 

4:50 9     22 

5.00 8     20 

5.50 7     18 

6.00 6i 16 

6.50 6     15 

7.00 5i 14 

8.00 5     12J 

9.00 4i 11 

10.00 4     10 

11.00 3i 9 

12.00 3i 8 

13.00 3     .. 7i 

14.00 21 7 

15.00 2i  ..  .- 6J 

16.00 2i 6 

18.00 2J    5i 

20.00.  . 2     5 

The  above  table  is  approximately  correct,  yet 
there  is  a  slight  difference  in  close  figuring,  but  is 
correct  as  far  as  the  optometrist  is  concerned;  for 
instance,  a  +  1-D.  lens  has-  a  focal  length  of  39 .  37 
in.,  while  we  call  it  40. 

Focus  (fo'-kus).  The  point  produced  by  rays  of 
light  passing  through  a  convex  spherical  lens  and 
coming  down  to  a  sharp  point  of  light.  • 

Folders.  A  term  employed  for  eye-glasses  that  can 
be  folded  up  and  placed  in  a  small  pocket. 

Follicle  (folMk-l).     A  small  secretory  cavity  or  sac. 


66  LEWIS  POCKET 

Follicular  (f ol-ik'-u-lar) .  Containing  foiiicles.  F. 
Conjunctivitis.  A  form  of  conjunctivitis  marked 
by  the  presence  of  follicles.  This  occurs  gener- 
ally in  children,  and  is  characterized  by  the  for- 
mation of  small,  clear  elevations,  consisting  of 
adenoid  tissue,  in  the  conjunctiva  of  the  lower 
lid;  in  some  cases  they  are  present  also  in  the 
retrotarsal  fold  of  the  upper  lid. 

S.     Fontana's  Canals  or  Spaces  (f on-tah'-nah) .     A  ring 
\       of  spaces  at  the  junction  of  the  cornea,  iris,  and 
sclera.     (See  Glaucoma.) 

Foramen  (fo-ray'-men)   (Optic).      Opening  for  pas- 
^         sage    of   optic   nerve   and   ophthalmic   artery   at 
apex  of  orbit. 

Fornix  Conjunctiva.  The  turn  or  fold  of  the  con- 
junctiva. 

Fossae  Patellaris  (pa-tel-Ia'-ris)  (meaning  dish-like 
depression).  The  depression  in  the  anterior  sur- 
face of  the  vitreous  body  in  which  the  crystalline 
lens  lies.     Also  called  the  Hyaloid  Fossa. 

\.  Fovea  (f  oh'-ve-ah) .  A  small  depression.  F.  Centra- 
lis is  employed  to  designate  the  little  depression 
in  the  center  of  the  macula  lutea. 

Frame  Fitting.  There  are  times  when  patients  com- 
plain that  their  glasses  are  not  comfortable,  yet 
they  have  the  right  correction.  The  cause  of  the 
trouble  is  sometimes  found  in  the  improper  adjust- 
ment of  the  frames.  The  fitting  of  a  frame  is 
very  important,  and  if  neglected  will  sometimes 
destroy  the  benefit  of  the  most  carefully  fitted 
lenses.  When  a  student  understands  the  relation 
between    accommodation    and    convergence    the 


Ol^TlCAL  DICTIONARY .  6'. 

value  of  frame-fitting  becomes  easily  understood. 
A  convex  lens,  with  its  curved  surfaces,  may  be 
described  as  made  up  of  an  infinite  number  of 
prisms  with  their  bases  meeting  at  the  center;  a 
concave  lens,  in  a  like  manner,  is  made  up  of  an 
infinite  number  of  prisms  with  their  bases  out- 
ward. When  a  person  looks  through  the  inner 
side  of  a  convex  lens,  as  he  is  compelled  to  do 
when  the  frames  are  too  wide  for  the  pupillary 
distance,  he  is  looking  not  only  through  convex 
lenses,  but  also  through  prisms  with  their  bases 
outward;  when  the  frames  are  too  narrow  he 
looks  through  prisms  with  their  bases  inward. 
With  concave  lenses,  of  course,  this  condition  will 
be  reversed,  and  besides  giving  a  prismatic  effect, 
will  cause  the  unbalancing  of  accommodation 
and  convergence. 

The  subject  of  frame-fitting  has  always  been 
and  always  will  be  more  or  less  of  a  problem  to 
the  student,  but  after  a  little  practice  and  careful 
attention  it  becomes  a  very  easy  matter.  I  will 
here  mention  a  few  points  which  may  be  of  assist- 
ance to  my  fellow-student. 

1st.  See  that  the  pupillary  distance  is  correct 
and  that  the  patient  is  looking  through  the  center 
of  lenses.  If  glasses  are  to  be  worn  constantly 
it  is  best  for  the  adjuster  to  stand  off,  say  about 
three  feet,  and  direct  the  patient  to  look  between 
his  eyes,  so  adjusting  frames  that  the  patient  will 
be  looking  through  the  centers  of  lenses.  For 
reading  glasses  the  optical  centers  should  be  slight- 
ly closer  and  lower,  and  the  top  of  the  lenses  must 
be  inclined  forward,  so  as  to  be  as  near  as  possible 
at  right  angles  to  the  line  of  vision.  In  this  way 
better  vision  is  enjoyed. 


68  LEWIS  POCKET 

2d.  The  lenses  should  be  placed  as  near  the 
eye  as  the  lashes  will  permit. 

3d.  Never  prescribe  a  small  lens  for  a  large 
face  nor  a  large  lens  for  a  small  face,  but  always 
make  the  lenses  as  large  as  you  possibly  can  with- 
out interfering  with  the  patient's  appearance,  and 
at  the  same  time  see  that  the  pupillary  distance  is 
correct.  In  the  fitting  of  spectacles  see  that  the 
angle  of  crest  saddles  the  nose  nicely,  and  that 
the  temples  are  long  enough  to  go  around  the 
ear  without  showing  underneath.  See  that  the 
temples  are  not  too  far  from  the  face  and  at  the 
same  time  do  not  press  on  the  flesh.  If  you  de- 
sire to  tilt  the  lenses  do  not  bend  temples,  but 
bend  the  end  piece.  All  glasses  should  tilt  out- 
ward from  the  top,  but  reading  glasses  more  than 
distant  ones.  Cylinders  should  always  be  worn 
as  spectacles,  as  it  is  very  important  that  they 
should  be  held  in  their  correct  position. 

It  is  always  best  for  one  who  is  just  commencing 
to  practice  to  supply  himself  with  a  full  set  of 
measuring  frames.  They  are  put  up  and  sold  by 
all  wholesale  optical  houses.  The  optical  houses 
also  supply  cards  on  which  are  printed  the  vari- 
ous dimensions.  Then  by  finding  a  sample  frame 
among  your  set  that  about  fits  your  patient  you 
lay  it  down  on  the  card,  allowing  for  any  change 
you  wish  to  make,  and  you  can  easily  figure  the 
exact  dimensions. 
f  Fundus.  The  fundus  of  the  eye  is  the  solid  struc- 
ture seen  by  means  of  the  ophthalmoscope, 
namely,  the  retina,  the  blood-vessels,  and  the 
optic  disc,  collectively. 
Fuscin  (fus'-sin).  A  brown  pigment  of  the  retinal 
epithelium. 


\: 


OPTICAL  DICTIONARY.  69 

Cranglion  Ciliary  (gang''-gle-on) .  A  semi-inde- 
pendent nervous  center  in  the  posterior  part  of 
the  orbit. 

Qeometrical  Center.     A  point  midway  between  all 

5dges. 

Generic  Compounds.  Lenses  having  spherical 
and  cylindrical  curvatures  of  the  same  species; 
that  is,  both  convex  or  both  concave.  Con- 
trageneric  compounds  have  one  surface  convex, 
the  other  concave. 

Qlabel'la,  Glaberium.  Space  between  the  eye- 
brows. 

Gland.  A  secretory  organ.  Lacrimal  g.,  the  gland 
which  secretes  the  tears. 

Glass.  A  hard,  brittle,  artificial  substance 
formed  by  the  fusion  of  silica,  potash,  and  lead. 
Under  the  best  conditions  it  is  quite  transpar- 
ent. Nothing  definitely  is  known  as  to  its 
origin.  The  Egyptians  used  it,  and  glass  has 
been  discovered  amongst  the  ruins  of  Pompeii. 

The  media  out  of  which  lenses  are  made. 
Crown  glass  for  optical  lenses,  sometimes  com- 
bined with  flint  glass. 

Glaucoma  (glau-ko'-mah).  A  disease  of  the  eye 
characterized  by  increased  intraocular  tension. 
In  order  to  fully  understand  this  disease  it  will 
be  necessary  to  study  thoroughly  the  anatomy  of 
the  eye,  and  in  doing  so  pay  particular  attention 
to  Schlemm's  Canal  and  the  Spaces  of  Fontana, 
situated  in  the  first  tunic  between  the  sclerotic 
and  cornea.  These  canals  are  said  to  carry  away 
the  excess  of  aqueous  humor.  The  theory  most 
generally  accepted  is,  that  the  vitreous  humor 
is  formed  in  the  choroid  and  ciliary  body  and 
passes  through  the  hyaloid  membrane  into  the 
vitreous  cavity;  from  there  it  filters  through  the 
suspensory  ligaments  into  the  posterior  chamber. 


70  LEWIS  POCKET 

where  it  becomes  watery,  and  is  known  as  the 
aqueous  humor.  After  passing  through  the  pupil 
into  the  anterior  chamber  it  is  said  to  pass  through 
the  Spaces  of  Fontana  into  Schlemm's  Canal.  In 
this  way  one  can  readily  see  that  if  the  iris  was 
attached  to  the  lens,  as  it  is  in  cases  of  iritis,  or 
by  the  straining  of  the  ciliary  muscles,  as  in  hyper- 
metropia,  thus  closing  the  Spaces  of  Fontana,  the 
drainage  system  would  be  blocked,  while  the 
humors  continue  forming,  resulting  in  a  painful 
intraocular  pressure.  Glaucoma  may  be  divided 
into  two  kinds,  primary  and  secondary.  Primary, 
when  it  makes  its  appearance  in  a  healthy  eye,  or 
with  a  disease  like  cataract.  Secondary,  when 
caused  by  a  disease  like  iritis.  It  is  a  progressive 
disease,  and  unless  checked  by  treatment  ends 
in  permanent  blindness. 

V  Symptons  of  glaucoma.  (1)  Pain,  sometimes 
of  a  neuralgic  character.  (2)  Increased  tension 
of    the    eyeball,    sometimes  becoming   stonelike. 

(3)  Rapid  failing  of  the  power  of  accommodation. 

(4)  Dimness  of  vision.  The  pupil  is  dilated  and 
sluggish.  (5)  The  patient  complains  of  seeing 
flashes  of  light  and  colored  halo  around  a  flame 
or  candle.  (6)  Cupping  of  the  optic  disc. 
(7)  Conjunctivitis.  The  iris  also  appears  steamy. 
When  glaucoma  is  suspected  the  patient  should 
be  sent  to  an  oculist  at  once. 

The  use  of  atropine  causes  the  iris  to  crowd 
into  the  periphery  of  the  anterior  chamber,  some- 
what occluding  the  Spaces  of  Fontana  and  inter- 
fering with  the  free  exit  of  aqueous  humor.  As 
the  intraocular  tension  increases,  the  stoppage 
becomes  more  complete.  When  the  atropine  is 
discontinued  the  sphincter  muscle  of  the  pupil 


OPTICAL  DICTIONARY.  71 

draws  the  iris  away  from  the  Spaces  of  Fontana 
and  the  normal  outlet  is  again  opened.  As  age 
advances,  the  sphincter  loses  its  power,  and 
frequently  in  old  people  fails  to  pull  the  iris  away 
from  the  Spaces  of  Fontana,  and  this  condition 
may  result  in  glaucoma.  For  the  reasons  men- 
tioned it  is,  as  a  rule,  unsafe  to  use  atropine 
after  the  age  of  from  30  to  35. 

Glaucomatous  (glau-kom'-at-ous).  Of  the  nature 
of  glaucoma. 

Glioma  (gly-oh'-mah) .  A  malignant  tumor  of  the 
retina. 

Gliosarco'ma.     Glioma  combined  with  sarcoma. 

Globulin  (glob'-u-lin) .     A  proteid  from  the  lens. 

Goggles.     Spectacles  with  wire  screens  for  the  eyes. 

Goiter  (goi'-ter).  An  enlargement  of  the  thyroid 
gland.  Exophthalmic  g.  (See  Exophthalmic 
Goiter.) 

Graduated  Tenotomy.  An  incomplete  cutting  of 
the  tendon  of  an  eye  muscle. 

Granular  Lids  (Trachoma).  Roughness  and  sore- 
ness of  the  inside  of  the  eyelids.  This  roughness 
is  caused  by  a  swelling  of  the  lymph-corpuscles, 
forming,  as  it  were,  little  lymphatic  glands  oi 
lymphatic  follicles. 

Gran'ulc.     A  small  rounded  body.     G.  Layer,  one 

of  the  layers  of  the  retina.  . 


72  LEWIS  POCKET 

xialler's  Circles.  Arterial  and  venous  circles 
within  the  eye. 

Ha'lo  Glaumato'sus.  A  whitish  ring  around  the 
optic  disc  in  glaucoma. 

Ha'lo  Symptom.  Seeing  of  colored  rings  around 
lights.     This  is  a  symptom  of  ircipient  glaucoma. 

Hec'tometer.     One  hundred  meters. 

Helcol'ogy.     Science  of  ulcers. 

Helco'sis.     The  formation  of  an  ulcer. 

Hemeralopia  (hem-er-al-o'-pi-ah) .  An  inability  to 
see  at  night. 

Hemiachromatopsia  (hem-i-a-chro-mat-op'-si-ah) . 
Color-blindness  in  one-half,  or  in  corresponding 
halves,  of  visual  field. 

Hemianopia    (hem  -  i  -  an  -  o'-  pi  -  ah) ,    Hemianopsia. 

Blindness  for  one-half  the  field  of  vision  in  one  or 
both  eyes. 

Hemiopic  (hem-e-op'-ik).  That  condition  which 
affects  one  eye  only. 

Hemophtharmia,  Hemophthal'mus.  Extravasation 
of  the  blood  inside  of  the  eye. 

Hemorrhage  (hem'-or-aj).  Escape  of  blood  from 
the  veins  or  arteries. 

Hering's  Theory.  This  is  a  doctrine  which  holds 
that  color-perceptions  are  dependent  on  a  visual 
substance  in  the  retina,  which  is  variously  modi- 
fied by  anabolism  for  black,  green,  or  blue,  and 
by  catabolism  for  white,  red,  and  yellow. 


V 


OPTICAL  DICTIONARY.  73 

Heterochromia  (het-er-o-kro'-me-ah) .  A  difference 
in  color  (in  the  irides  or  of  different  parts  of  the 
same  iris). 

Heteronymous  (het-er-on'-im-us) .  Crossed.  (See 
Diplopia.) 

Heterophoria  (het-er-o-pho'-ri-a) .  A  tendency  cf 
the  visual  lines  away  from  parallelism.  It  is 
subdivided  into  eight  kinds.  When  the  eyes  have 
a  tendency  to  turn  in  it  is  known  as  esophoria; 
if  a  tendency  to  turn  out,  it  is  known  as  ex- 
ophoria;  if  a  tendency  to  turnup,  it  is  known  as 
hyperphoria;  if  up  and  in,  hyperesophoria, 
and  if  up  and  out,  hyperexophoria;  if  a  ten- 
dency downward,  it  is  known  as  cataphoria;  and 
if  down  and  in,  esocatophoria;  if  down  and  out, 
exocatophoria.  Any  error  of  refraction  is  liable 
to  bring  on  Heterophoria,  and  by  correcting  the 
error,  the  Heterophoria  will  disappear,  though 
it  may  linger  for  a  month  or  two. 

Heterophthal'mos.  That  condition  in  which  the 
irides  differ  in  color. 

Heterotropia  (het-er-o-tro'-pi-a)  (Strabismus).  This 
term  expresses  a  stronger  meaning  than  hetero- 
phoria, where  there  is  merely  a  tendency,  while  in 
heterotropia  there  is  a  positive  and  visible  ap- 
pearance of  the  eyes  turning,  and  they  may  turn 
in  any  direction,  as  in  heterophoria.  When  the 
eye  turns  up  it  is  hypertropia;  if  downward, 
catatropia;  if  inward,  esotropia;  if  outward, 
ex  otropia. 

Hippus  (hip'-us) .  Spasmodic  pupillary  movements^ 
independent  of  the  action  of  light. 


7*  LEWIS  POCKET 

Holmgren's  Test  (holm'-grens) .  A  color  test  with 
a  number  of  different  colored  yarns  representing 
the  various  shades  of  different  colors.  Used  for 
detecting  color-blindness. 

Homocentric  Rays  (ho-mo-sen'-tric).  A  conic  pen- 
cil of  light-rays. 

Homonymous.     (See  Diplopia.) 

.Hordeolum  (hawr-dee'-o-lum).     Sty;    inflammation 

V  of  sebaceous  glands  of  the  eyelid. 

Horny  Epithelium.     Trachomatous  conjunctivitis. 

Horopter  (ho-rop'-tur) .  The  field  of  binocular 
vision  as  seen  with  the  eyes  fixed. 

Hot  Eye.  Temporary  congestion  of  the  eye.  This 
is  seen  in  gouty  patients. 

Humor.     A  fluid  element  of  the  eye      (Aqueous, 

crystalline  lens,  and  vitreous.) 

Hyaline  (hi'-al-in).     Glassy. 

Hyalitis  (hy-al-i'-tis) .  Inflammation  of  the  vitreous 
humor  or  hyaloid  membrane. 

Hyaloid  (hy'-al-oid) .     That  which  resembles  glass 

V  in  its  transparent  quahties.  Hyaloid  membrane 
surrounds  and  encloses  the  vitreous  humor  and 
forms  the  suspensory  ligaments. 

\^  Hyaloid  Artery.     The  fetal  branch   of  the  central 
*^     artery  of  the  retina. 

Hyaloid  Canal,  or  Canal  of  Stilling.  The  canal 
through  the  vitreous  body,  occupied  by  the 
hyaloid  artery  during  fetal  life, 


\ 


OPTICAL  DICTIONARY.  76 

Hyaloid  Fossa.  The  depression  in  the  anterior  sur- 
face of  the  hyaloid  membrane  in  which  the 
crystalHne  lens  lies. 

Hyaloid  Membrane.  The  delicate  transparent  mem- 
brane which  forms  a  sac  and  contains  the  vitreous 
humor,  and  forms  the  suspensory  ligaments  of 
the  lens  and  the  Zone  of  Zinn. 

Hydrophthalmia  (hy-drof-thal'-mi-ah) ,  Hydroph- 
thalmus.  Increase  in  the  fluid  contents  of 
the  eye. 

Hydrops  (hi'-drops)  (dropsy).  An  abnormal  col- 
lection of  fluid  in  any  part  of  the  body. 

Hygroma  (hi-gro'-mah).  A  sac  or  cyst  filled  with 
fluid. 

Hyperaesthesia  (hi-per-as-the'-si-ah).  Over-sensi- 
tiveness. H.  of  Retina,  over-sensitiveness  of  the 
retina. 

Hyperemia  (hi-per-e'-me-ah) .  A  condition  where 
there  is  an  abnormal  fulness  of  the  blood-vessels. 
H.  of  the  eyelids  is  often  a  forerunner  of  inflam- 
mation. It  is  usually  accompanied  by  a  slight 
marginal  blepharitis  and  even  conjunctivitis,  and 
if  these  are  relieved  the  hyperemia  to  a  great  ex- 
tent will  disappear. 

Hyperkeratosis  (hy-per-ker-at-o'-sis) .  Hypertrophy 
of  the  cornea. 

Hypermetropia  (hy-per-me-tro'-pi-ah)  (far-sighted) . 
An  error  of  refraction,  where  parallel  rays 
of  light  focus  back  of  the  retina  with 
the  muscles  of  accommodation  at  rest.  Sub- 
divided    into     three    classes — latent,     manifest 


76  LEWIS  POCKET 

and  total.  Latent  h.  has  no  subdivisions;  it 
is  hypermetropia  that  is  hidden  by  cramp  of 
the  ciHary  muscle,  and  will  not  relax  without  the 
use  of  drugs  at  the  time  of  fitting,  but  when  the 
correction  for  the  manifest  is  worn,  the  cramp  be- 
gins to  relax  and  more,  hypermetropia  becomes 
manifest.  It  may  take  a  week  or  a  year.  Mani- 
fest h.  is  that  part  found  and  corrected  with 
the  trial  case  and  retinoscope.  It  is  said  to 
have  three  subdivisions,  namely,  facultative, 
relative,  and  absolute.  Facultative  h.  is  where 
the  patient  has  the  ability  to  overcome  his  error 


A  hypermetropic  eye.  The  heavy  lines  show  tne  focus  of 
parallel  rays  behind  the  retina.  The  dotted  lines  show  the 
effect  of  accommodation  upon  the  same  rays. 

by  accommodation,  and  sees  well  at  all  distances. 
Classes  relieve  strain,  but  do  not  improve  vision 
in  this  case.  Relative  h.  is  where  it  is  possible  to 
accommodate  for  a  near  point,  by  converging  to 
a  point  still  nearer — in  fact,  by  squinting.  This 
eye  has  blurred  vision  for  close  work,  and  plus 
spheres  improve  vision.  Absolute  h.  is  where  the 
error  exceeds  the  amount  of  the  accommodation, 
and  the  patient  is  unable  to  bring  the  focus  to 
the  retina,  and  vision  is  blurred  at  all  distances. 


OPTICAL  DICTIONARY.  77 

The  correction  always  improves  vision.  Total  h. 
is  the  full  amount  of  hypermetropia  the  patient 
has.  For  instance,,  we  correct  the  eye  with  the 
trial  case  and  find  2-D.  of  manifest;  then  by  the 
use  of  drugs  relax  any  cramp;  and  now  find  that 
the  same  eye  has  6-D.  of  hypermetropia.  4-D. 
was  hidden  by  cramp.  This  we  call  latent,  6-D. 
being  the  total  amount  of  hypermetropia. 

Hyperope   (hi'-per-op) .     A  person  who  has  hyper- 
metropia. 

Hyperopia  (hi-per-o'-pe-ah).     (See  Hypermetropia.) 

\  Hyperphoria     (hy-per-f  o'-ri-ah) .     The    tendency   of 
elevation  of  one  visual  axis  above  the  other. 

Hyperplasia    (hi-per-pla'-ze-ah) .     Excessive    tissue 
formation. 

Hypertropia   (hy-per-tro'-pi-ah).     Elevation  of  one 
visual  axis  above  the  other. 

Hypertrophy     (hy-per'-tro-f  y) .     An    abnormal    in- 
crease in  the  size  of  a  part  or  an  organ. 

Hyphemia  (hi-f e'-me-ah) .      Hemorrhage  within  the 
eye. 

Hypnogenet'ic.     Causing  or  producing  sleep. 

Hypnolepsy  (hip'-no-lep-se) .     Abnormal  sleepiness. 

Hypometropia  (hy-po-me-tro'-pi-ah).     (See  Myopia 
and  Brachymetropia.) 

V  Hypophoria    (hi-po-f o'-re-ah) .  ,   A    tendency    of    a 
visual  line  downward. 


79  LEWIS  POCKET 

Hypopyon  (hi-po'-pe-on) .     Pus  in  the  anterioi  oiiam- 
ber  of  the  eye. 

Hypotonia     (hi-po-to'-ne-ah).       Diminished     intra- 
ocular tension. 

Hypotonus    (hi-pot'-o-nus).     (See   Hypotonia.) 

Hypotony  (hi-pot'-o-ne) .     (See  Hypotonia.) 


Xdentical  Points.  When  the  image  falls  on  corre- 
sponding points  on  the  retinae  of  the  two  eyes. 

Iliaqueation  (il-lak-we-a'-shun) .  The  curing  of  in- 
growing eyelashes  by  drawing  with  a  loop. 

Illumination  (il-lu-min-a'-shun) .  The  lighting  up  of 
a  place  or  object  for  inspection.  Focal  i.,  when 
light  is  brought  to  a  focal  point  by  lens  or  mirror. 
Axial  Uy  when  light  is  transmitted  or  reflected 
along  the  axis  of  a  lens.  Direct  i.,  light  thrown 
directly  upon  the  object.  Oblique  i.,  when  an 
object  is  illuminated  from  one  side. 

Illusion  (il-lu'-zhun) .  An  unreal  image  presented 
to  the  mental  vision. 

Image  (im'-ej).  A  picture  or  conception  of  any- 
thing real.  Aeri^^.,  image  seen  as  in  the  air  by 
the  ophthalmoscopeSsj  Direct  i.,  Erect  i.,  and 
Virtual  i.,  formed  by  rays  not  yet  focused.  An 
upright  imag^M  False  i.,  image  formed  on  the 
retina  of  the  deviating  eye  in  strabismus. 
Optical  i.,  an  appearance  of  an  object  created  by 
refraction  or  reflection. 

Inad'equacy.     Unable  to  perform'  allotted  functijn 


\ 


OPTICAL  DICTIONARY.  79 

m  cideiit  Ray.     The  name  given  to  a  ray  of  light 
before  it  strikes  the  second  medium. 


Index  of  Refracting.  The  refracting  or  bending 
y  power  of  the  medium  as  compared  with  air, 
the  normal  standard,  and  the  index  of  which  is 
the  unit  1.  Water  as  compared  with  air  is  1.33; 
crown  glass  1.52;  flint  glass  1.62 +  ;  pebble,  1.54; 
diamond,  2.4,  the  greatest  index  of  any  known 
medium.  The  transparent  parts  of  the  eye  in 
their  order  are  as  follows:  the  cornea,  1.33;  the 
aqueous  humor,  1.33;  the  crystalline  lens,  1.43;  and 
the  vitreous  humor,  1.33. 

i  Infinite  Distance.     When  rays  of  light  proceed  from 
V    a  distance  of  twenty  feet  or  more  they  are  con- 
sidered parallel,  and  are  said  to  come  from  in- 
finity. 

Inflammation  (in-flam-ma'-shun).  A  diseased  con- 
dition characterized  by  redness,  pain,  heat,  and 
swelling.  Traumatic  i.,  that  which  follows  a 
wound  or  injury „ 

Infraduction,  Deorsumvergence.  The  power  of  the 
inferior   rectus   muscles. 

Infraorbital  (in-f  ra-or'-bi-tal) .  Situated  beneath 
the  orbit. 

J[nstrunients  and  their  uses. 

N^  Amblyoscope — An  instrument  to  stimulate,  ex- 
ercise, and  develop  the  fusion  faculty  in  strabis- 
mus, or  squinting  patients. 

Color  Test  (Holmgren's) — A  set  of  worsteds, 
consisting  of  various  shades  and  tints,  for  testing 
color-blindness. 


80  LEWIS  POCKET 

Deviometer — An  instrument  for  determining 
the  degree  of  deviation  in  strabismus,  or  squint. 

Keratometer — (See  Ophthalmometer.) 

Latest  Optometer — An  instrument  combining 
the  advantages  of  a  fixed  and  revolving-cell  trial 
frame,  Stevens  Phorometer,  Rotary  Prism,  and 
Maddox  Multiple  Rod. 

Ophthalmoscope — An  instrument  with  which 
the  interior  of  the  eye  may  be  examined.  Also 
the  dioptric  and  pathological  states  may  be  deter- 
mined. There  are  many  different  kinds  of  oph- 
thalmoscopes; for  instance,  the  Loring  is  a  small 
hand  affair,  which  contains  a  mirror  and  a  number 
of  lenses;  the  self-luminous,  by  DeZeng,  also  a 
hand  instrument;  and  the  combined  ophthalmo- 
scope and  retinoscope,  a  combined  instrument 
for  indirect  ophthalmoscopy  and  for  retinos- 
copy.  This  is  a  large  machine  which  stands  on 
a  table. 

Ophthalmometer  or  Keratometer — An  instru- 
ment for  determining  the  amount  and  axis  of 
corneal  astigmatism,  an  objective  test. 

Ophthalmometroscope  —  An      ophthalmoscope 
with  an  attachment  for  measuring  the  refraction 
s       of  the  eye. 

^      Perimeter — An  instrument  for  measuring  the 
visual  field. 

Punctumeter — A  simple  instrument  for  deter- 
mining the  far  point  and  the  near  point,  there- 
fore the  amount  of  hypermetropia,  myopia,  or 
presbyopia.  It  also  indicates  the  age  of  the 
patient. 

Savage  Monocular  Phorometer  and  Cyclo- 
Phorometer — Two    instruments    which    together 


OPTICAL  DICTIONARY.  81 

ixiake  a  complete  appliance  for  measuring  all  of 
the  muscles  of  the  eye. 

Self- Luminous  Retinoscope — An  instrument  for 
retinoscopy,  self -lumina ted. 

Skiascope — A  frame  with  a  series  of  plus  and 
minus  spherical  lenses,  to  be  used  in  place  of  test 
frame  and  lenses  when  refracting  a  patient  by 
retinoscopy. 

Stevens  Phorometer — An  instrument  for  meas- 
uring muscular  imbalance. 

Stigmatometer — An  instrument  for  testing  re- 
fraction of  the  eye  by  the  objective  method. 
Also  a  complete  ophthalmoscope  for  the  direct 
examination. 

InsuflBlciency.     Incapacity  of  normal  action  within 

the  eye. 

Intercilium  (in-ter-sil'-e-um) .  The  space  between 
the  eyebrows. 

Interorbital  (in-ter-or'-bi-tal).  Situated  between 
the  orbits. 

Inter'nus.  Internal.  The  internal  rectus  muscles 
of  the  eye. 

Interval,  Sturm's,  or  Focal  i.  In  astigmatism,  is 
the  distance  between  the  two  foci,  at  which  the 
principal  meridians  meet. 

Intraocular  (in-trah-oc'-u-lar) .     Situated  within  the 

globe  of  the  eye. 
intraocular     Tension.     Pressure     from     the     fluids 

within  the  eye. 

Intraorbital     (in-trah-or'-bit-al) .     Situated     within 

the  orbit. 
Ir'idal.     Pertaining  to  the  iris. 


82  LEWIS  POCKE 

Iridectome  (ir-id-ek'-tom).  An  instrument  used 
in  cutting  the  iris  in  iridectomy. 

Iridectomize  (ir-id-ek'-tom-ize) .  To  cut  away  a 
part  of  the  iris. 

Iridectomy  (ir-id-ek'-tormy) .  The  operation  for  re- 
moving a  piece  from  the  iris  for  the  reHef  of  ten- 
sion of  the  eyeball  in  the  case  of  glaucoma,  thus 
producing  an  artificial  pupil. 

f ridencleisis  (ir-id-en-cli'-sis) .  An  operation  for  dis- 
placing the  pupil  from  its  natural  position,  brought 
about  by  drawing  the  iris  into  a  wound  made 
near  the  periphery  of  the  cornea,  and  causing  it 
to  become  adherent  there. 

Irideremia  (ir-id-er-e'-mi-ah) .  Defect  or  imperfect 
condition  of  the  iris. 

Irides  (ir'-id-ez).     Plural  of  iris. 

Iridesis  (ir-id'-e-sis) .  Strangulation  of  a  part  of 
the  iris  to  form  an  artificial  pupil. 

Iridescent  Vision.  That  condition  in  which  vari- 
ously hued  borders  are  seen  surrounding  artificial 
light. 

Iridic  (i-rid'-ik).     Pertaining  to  the  iris. 

Iridoavulsion  (ir'-i-doh-a-vul'-shun) .  A  term  ap- 
plied to  the  total  removal  of  the  iris  when  it  is 
completely  torn  from  its  periphery. 

Iridocele  (i-rid'-o-sele) .  Hernial  protrusion  of  a 
slip  of  the  iris. 

Iridochoroiditis  (ir-.id-o-ko-roid-i'-tis).     Inflamma- 
tion of  the  iris  and  choroid. 


OPTICAL  DICTIONARY.  83 

Iridocinesis  (ir-id-o-sin-e'-sis).  The  movement  of 
the  iris  in  contracting  and  expanding. 

Iridocyclitis  (ir-id-o-syc-li'-tis) .  Inflammation  of 
the  iris  and  ciliary  body. 

Iridod'esis.  That  condition  in  which  a  loop  of  iris 
is  drawn  out,  and  strangulated  by  a  fine  ligature 
tied  around  it  over  the  incision;  the  little  loop 
soon  drops  off,  and  the  result  is  a  pear-shaped 

.   pupil,  with  its  broad  end  toward  the  center. 

Iridodialysis  (ir-id-o-di-al'-ys-is) .  Separation  of  the 
iris  from  the  ciliary  body. 

Iridodonesis  (ir-id-o-do-ne'-sis) .  Trembling  condi- 
tion of  the  iris. 

IridoDcus  (ir-id-on'-kus) .  A  tumor  or  swelling  of 
the  iris. 

Iridoperiphacitis  (ir-id-o-per'-i-f a-si'-tis) .  Inflamma- 
tion of  the  capsule  of  the  lens  of  the  eye. 

Iridoplania  (ir-id-o-pla'-ni-ah) .  Trembling  of  the 
iris;   iridodonesis. 

Iridoplegia  (ir-id-o-ple'-gi-ah) .  Paralysis  of  the  iris. 
Without  defect  of  accommodation,  it  usually 
affects  only  the  action  to  light,  reflex  iridoplegia, 
the  associated  action  remaining.  It  occurs  as  a 
very  early  symptom  in  locomotor  ataxia,  some- 
times without  any  other  symptoms  of  that  dis- 
ease, and  should  always  lead  to  full  investigation. 
It  is  probably  due  to  degeneration  in  that  part 
of  the  nucleus  of  the  third  nerve  which  presides 
over  the  reflex  action  of  the  pupil. 


\, 


^  LEWIS  POCKET 

Iridorrhexis  (ir-id-or-rhex'-is) .  Rupture  of  the  iris. 
Tearing  away  of  the  margin  of  the  iris. 

Iridosclerot'omy.  Puncture  of  the  sclerotic  and  of 
the  edge  of  the  iris. 

Iridotomy  (ir-id-ot'-o-my) .  The  operation  whereby 
an  artificial  pupil  is  formed  by  the  natural  gaping 
of  a  simple  incision  in  the  iris.  Iridotomy  is  most 
useful  when  the  iris  has  become  tightly  drawn 
toward  the  operation  scar  by  iritis  occurring  after 
a  cataract  has  been  removed. 

I'ris.  That  part  of  the  second  tunic  which  is  located 
in  front  of  the  crystalhne  lens  and  gives  the  eye 
its  color  and  regulates  the  amount  of  light  which 
enters.  It  contains  two  muscles,  the  circular  (or 
sphincter),  which  surrounds  the  pupil,  and  is 
supplied  by  the  third  nerve;  the  radiating  muscle 
(or  dilater),  which  is  chiefly  supphed  by  the  sym- 
pathetic. The  iris  is  suspended  in  the  aqueous 
humor,  which  fills  the  space  between  the  cornea 
and  the  lens,  thus  forming  the  anterior  and  pos- 
terior chambers. 

Iris  Shadow.  The  test  for  maturity,  or  ripened 
cataract;  created  by  oblique  illumination. 

Iritic  (i-rit'-ik).     Pertaining  to  the  iris. 

Iritic  Angle.  The  angle  formed  by  the  junction 
of  the  iris   and  cornea. 

Iritis  (i-ri'-tis).  Inflammation  of  the  iris,  which  is 
usually  caused  by  certain  specific  blood  diseases. 
It  often  occurs  in  the  course  of  ulcers  and  of 
wounds  and  other  injuries  of  the  cornea;  also 
with  sclerotitis  and  keratitis.  ^ 


OPTICAL  DICTIONARY.  81 

Irregular  Astigmatism.     (See  Astigmatism.) 

Irritant.     Causing  irritation. 

Ischemia  (is-ke'-me-ah).     Bloodlessness. 

Ischemia  Retinae    (is-ke'-me-ah).      Diminution    oi 

arteries  in  the  retina. 

Isocoria  (i-so-co'-ri-ah) .     Where  the  pupils  in  the 
two  eyes  are  equal. 

Isometropia  (i-so-met-ro'-pi-ah) .     The  state  in  which 
both  eyes  are  alike  in  their  refraction. 


tJ  ager's  Test  Type.  The  standard  type  for  close 
print. 

Jeffrey's  Symptom.  That  condition  which  exists 
when  patient  suddenly  turns  his  eyes  upward  and 
there  is  absence  of  facial  contraction;  seen  in 
exophthalmic  goiter. 


\ 


-ki^eratalgia  (ker-at-al'-je-ah).     That  condition  in 
which  there  is  pain  in  the  cornea. 

Keratectasia    (ker-at-ek-ta'-si-ah) .     That   condition 
in  which  the  cornea  protrudes. 

Keratitis  (ker-at-i'-tis) .   Inflammation  of  the  cornea. 

Keratocele   (ker-at'-o-cele) .     Corneal  protrusion  of 
Descemet's  Membrane. 

Keratoconus  (ker-at-o-ko'-nus) .     That  conditibn  in 
which  there  is  a  conical  cornea. 


86  LEWIS  POCKET 

Keratoglobus  (ker-at-o-glo'-bus) .  A  globular  pro- 
trusion of  the  cornea. 

Keratohelcosis  (ker-at-o-hel-ko'-sis) .  That  condi- 
tion wherein  there  is  ulceration  of  the  cornea. 

Keratoiri'tis.  That  condition  wherein  the  cornea 
and  iris  are  inflamed. 

Keratomalacia  (ker-at-o-ma-la'-she-ah) .  Softening 
of  the  cornea. 

Keratome  (ker'-at-om) .  A  knife  for  incising  the 
cornea. 

Keratometer  (ker-at-om'-e-ter) .  An  instrument  used 
for  measuring  the  cornea.  It  is  commonly  called 
the  ophthalmometer,  of  which  there  are  several 
different  makes. 

Keraiometry    (ker-at-om'-e-try).     Measurement    of  • 
corneal  curves. 

Keratomycosis  (ker-at-o-my-ko'-sis) .  Fungous  dis- 
ease of  the  cornea. 

Keratonyxis  (ker-at-o-nik'-sis) .  Puncture  of  the 
cornea. 

Keratoplasty  (ker'-at-o-plas-ty) .  Plastic  surgery  of 
the  cornea. 

Keratoscope  (ker'-at-o-scope).  Instrument  for  ex- 
amining the  cornea. 

Keratoscopy  (ker-at-os'-ko-pe).  Examination  of  the 
cornea  with  a  keratoscope.     Skiascopy. 

Kerectomy  (ke-rek'-to-me).  Removal  of  part  of  tb^ 
cornea. 


OPTICAL  DICTIONARY  8V 

Kilometer.      One  thousand  meters. 

Kopiopia    or    Copiopia    (ko-pee-oh'-pee-ah) .      (See 
Asthenopia.) 

Koreetomia  or  Corectomia  (ko-rek-to'-mee-ah) .    The 
•  operation  for  artificial  pupil  by  removal  of  a  part 
of  the  iris. 

Korectopia  (kor-ek-to'pe-ah) .     Displacement  of  the 
pupil. 

Koroscopy  (ko-ros'-ko-pee) .     (See  Retinoscopy.) 


\^ 


-Liachrymal  Apparatus.  Consists  of  the  lachrymal 
gland  which  secretes  the  tears  and  the  exsecretory 
ducts  which  convey  the  fluid  to  the  surface  of  the 
eye.     This  fluid  after  passing  over  the  eye  run? 

.  through  the  puncta  into  the  lachrymal  canal, 
then  to  the  lachrymal  sac  and  along  the  nasal 
duct  into  the  cavity  of  the  nose. 

Lachrymal  (lak'-rim-al) .     Pertaining  to  tears. 

Lachrymation  (lak-rim-a'-shun) .  The  secretion  and 
discharge  of  tears. 


88  LEWIS  POCKET 

Lachrymotomy  (lak-rim-ot'-o-my) .  Operation  for  in- 
cision of  lacrimal  duct  or  sac. 

Lacrimal,   Lacrymai.     (Same   as   Lachrymal.) 

Lacu'nar  Orbitae.     The  roof  of  the  orbit  of  the  eye. 

^  La^cus   Lacrima'lis.     The   triangular   space   at   the 
inner  canthus  between  the  two  eyelids. 

Lagophthalmus  (lag-of-thar-mus) .     That,  condition 
in  which  it  is  impossible  to  close  the  eyes. 

Lakus.     The  small  circular  portion  at  the  nasal  side 
of  the  opening  between  the  eyelids. 

Lamina  (lam'-in-a) .     A  layer  consisting  of  a  flat, 
thin  membrane. 


N^' 


I^amina  Cribrosa  (lam'-in-a  crib-ro'-sa) .  The  per- 
forated area  in  the  sclerotic  through  which  the 
optic  nerve  fibers  pass  to  form  the  retina. 


Lamina  Fus'ca.     The  outside  layer  of  the  choroid. 

Landolt,  Edmund,  M.  D.  Ophthalmologist,  born  in 
Aaran,  Switzerland,  in  1846;  pursued  his  profes- 
sional studies  in  the  universities  of  Heidelberg, 
Vienna,  BerHn,  Utrecht,  and  Zurich,  graduating 
from  the  latter  in  1869;  then  worked  for  more  than 
a  year  as  Horner^s  assistant  in  the  Zurich  clinic 
for  eye  diseases;  in  1874  he  established  himself 
in  Paris  as  an  ophthalmologist.  His  investiga- 
tions in  his  specialty  have  been  distinguished  by 
their  originality.  Among  his  works  are  ^^On  the 
Retina,'^  **A  Manual  of  Ophthalmoscopy,*^  pub- 
lished in  French,  EngUsh,  German,  and  Spanish, 
*'The  Refraction  and  Accommodation  of  the  Eye." 


OPTICAL  DICTIONARY.  89 

Lapsus  (lap'-sus).  The  dropping  of  the  upper  lid, 
produced  by  a  paralysis  of  the  levator  palpebra 
muscle.     Synonym,   Ptosis. 

Lashes.     The  name  given  to  the  hairs  of  the  eyelids. 

Latent  (la'-tent).  That  which  is  not  apparent  or 
manifest.     (See  Hypermetropia.) 

Layer.  A  stratum  having  a  certain  amount  of  thick- 
ness and  serving  the  purpose  of  a  covering. 

Leber's  Disease  (La'-berz).  Atrophy  of  the  optic 
nerve,  which  is  hereditary. 

Lema  (le'-ma).  The  dry,  hard,  yellowish  incrusta- 
tions which  collect  in  the  inner  canthus. 

Lens.  The  term  lens  w^s  first  applied  to  any  trans- 
y  parent  refracting  body  which  had  two  spherical 
surfaces,  on  account  of  its  resemblance  to  a  vege- 
table known  as  a  lentil.  A  lens  is  a  transparent 
substance,  crown  or  flint  glass  chiefly,  through 
which  an  object  may  appear  to  be  increased  or 
decreased  in  size,  and  may  have  either  convex  or 
concave  spherical  or  cylindrical  surfaces.  There 
are  six  varieties  of  spherical  lenses — three  plus 
and  three  minus — all  of  which  can  be  made  the 
same  dioptric  power,  the  only  difference  being  in 
the  shape  of  the  lens.  Plus  or  positive  lenses  are 
thickest  in  the  center.  Minus  or  negative  lenses 
are  thinniest  at  their  centers.  A  plus  sphere  wil) 
refract  the  same  in  all  its  meridians  and  converge 
parallel  rays  to  a  point  or  focus,  while  a  minus 
sphere  will  diverge  parallel  rays  from  a  point. 


90 


LEWIS  POCKET 


The  different  forms  of  plus  and  minus  spLorical 
lenses  are  here  represented: 


A 


V 


A.  Piano  Convex. 

B.  Biconvex. 

C.  Periscopic  Convex. 


D.  Piano  Concave. 

E.  Biconcave. 

F.  Periscopic  Concave. 


A  line  passing  through  the  optical  center  at 
right  angles  to  the  surfaces  of  these  lenses  is  not 
refracted,  and  is  known  as  the  principal  axis, 
while  all  other  rays  undergo  more  or  less  refrac- 
tion. A  secondary  axis  is  any  line  which  crosses 
the  principal  axis  at  the  optical  center  of  a  lens. 
It  is  not  a  straight  line,  but  a  refracted  one,  and 
on  emerging  takes  a  direction  parallel  to  that 
which  it  would  have  pursued  had  it  not  been 
interrupted  by  the  lens.  Cylindrical  1.,  a  lens  with 
refractive  power  in  all  meridians  but  one.  This 
one  is  known  as  the  axis,  and  is  nothing  more  than 
piano  glass.  The  refraction  varies  from  zero  at 
the  axis  to  the  full  strength,  which  is  at  right  angles 
to  the  axis.  Crystalline  1.,  the  lens  of  the  eye 
which  resembles  a  crystal.  A  transparent  double 
convex  lens  situated  in  its  capsule  behind  the 
pupil  between  the  aqueous  and  vitreous  humor, 
and  when  in  a  state  of  rest  has  a  focal  strength 
of  from  plus  19  to  plus  20  diopters.  Compound  1., 
a  lens  consisting  of  two  or  more  lenses  made  up 


OPTICAL  DICTIONARY.  91 

together,  such  as  a  sphere  and  a  cylinder.  Toric 
1.,  a  lens  with  power  in  all  meridians,  but  of  differ- 
ent amounts  on  the  same  side,  usually  made  extra 
deep  periscopic.  Periscopic  1.,  a  lens  having  a 
convex  and  concave  surface.  Achromatic  1.,  a 
lens  composed  of  two  pieces,  one  of  crown  and  the 
other  of  flint  glass;  the  former'one  being  plus  and 
the  latter  minus,  and  only  half  as  strong  in  its  re- 
fractive power,  but  of  equal  dispersive  power,  and 
overcomes  chromatic  aberration.  Aplanatic  1.  is 
on  the  order  of  the  achromatic  lens,  except  that  the 
minus  is  divided  and  placed  half  on  each  side  of 
the  plus.  In  this  way  not  only  the  chromatic 
but  the  spherical  aberration  is  overcome,  and  a 
perfect  lens  formed.  They  are  used  for  high- 
power  instruments.  Bifocal  1.  (see  Bifocal). 
Lenticular  1.  is  a  lens  which  is  piano  at  the 
edges,  and  the  power  is  ground  in  a  space  of 
about  half  an  inch  in  diameter  in  the  center. 
When  a  plus  lens  is  required  it  is  made  in  the 
form  of  a  scale  and  cemented  on  a  piano  or 
simple  cylinder.  In  this  way  we  do  away  with 
the  thick  edge  of  a  high-power  minus  lens,  and 
it  also  makes  up  in  a  thinner  form  for  a  high- 
power  plus,  but  they  are  never  made  up  in  weak 
lenses.  Orthoscopic  1.,  a  lens  with  two  elements 
a  sphere  and  a  prism,  so  arranged  that  the  amount 
of  accommodation  and  convergence  should  ex- 
actly correspond. 

Lens  Capsule.  A  transparent,  highly  elastic  and 
brittle  membrane  which  encloses  the  crystalline 
lens.  It  rests  in  a  depression  of  the  vitreous  body 
just  behind  the  iris,  and  is  held  in  position  by  the 
suspensory  ligaments. 


92  LEWIS  POCKET 

Lenticonus  (len-tik-o'-nus) .  Exaggerated  curva- 
ture of  the  crystalline  lens. 

Lenticular  Astigmatism.     (See  Astigmatism.) 

Lenticular  Ganglion  (len-tik'-u-Jar  gang'-gle-on) .  A 
small  reddish  body  near  the  back  part  of  the 
orbit,  between  the  optic  nerve  and  the  external 
rectus  muscle. 

Leucoma  (lew-ko'-mah).     (See  Leukoma.) 

Leukoma  (leu-ko'-ma).  White  corneal  opacity.  Al- 
bugo. 

Le'sion,     Any  hurt,  wound,  or  local  degeneration. 

Levator  Palpebra  Muscle  (le-va'-tor  pal'-pe-bra 
mus'-l).     (See  Muscles.) 

Ligament  (lig'-a-ment) .  A  tough  band  of  connec- 
tive tissue,  the  purpose  of  which  is  to  connect  the 
bones  together  or  surround  them  as  a  capsule. 
There  are  several  ligaments  concerned  in  the 
anatomy  of  the  eye.  Ciliary  Ligament,  Palpebral 
Ligament,  External  Palpebral  Ligament,  Internal 
Palpebral  Ligament,  Suspensory  Ligament  or 
Zone  of  Zinn,  Ligament  of  Zinn.  The  Ciliary 
1.,  or  circle  (annulus  albidus),  is  the  bond 
of  union  between  the  external  and  middle 
tunics  of  the  eyeball,  and  serves  to  connect  the 
cornea  and  sclerotic,  at  their  line  of  junction, 
with  the  iris  and  external  layer  of  the  choroid. 
It  is  also  the  point  to  which  the  ciliary  nerves 
and  vessels  proceed  previously  to  their  distribu- 
tion, and  it  receives  the  anterior  ciliary  arteries 
through  the  anterior  margin  of  the  sclerotic. 
A  minute  vascular  canal  is  situated  within  the 
ciliary  ligament,  called  the  ciliary  canal,  or  the 


OPTICAL  DICTIONARY.  93 

Canal  of  Fontana,  from  its  discoverer.  The 
Palpebral  1.  joins  the  cartilage  of  the  lids 
to  the  orbit  the  same  as  the  tarsal  ligament. 
The  External  Palpebral  1.  unites  the  lid  to  the 
outer  edges  of  the  orbit.  The  Internal  Palpebral 
1.  covers  an  area  including  the  upper  maxilla 
to  the  inner  margin  of  the  lid.  The  Suspensory 
I.,  or  Zone  of  Zinn,  surrounds  the  crystalline 
lens  and  holds  it  in  place  within  the  circle  of  the 
muscle  of  accommodation. 

Ligament  of  Zinn.  A  circular  ligament  which  is 
attached  to  the  bone  at  the  optic  foramen,  from 
which  arises  the  four  recti  muscles  and  the 
superior  oblique. 

Light.  Light  is  that  physical  force  which,  acting 
upon  the  sensitive  elements  of  the  retina,  excites 
in  the  mind  the  impression  of  vision  (or  vibrations 
of  ether),  and  is  made  up  of  rays,  beams,  and 
pencils. 

A  Ray  is  the  smallest  visible  line  of  light. 

A  Beam  is  ti  collection  or  bundle  of  parallel 
rays. 

A  Pencil  is  a  number  of  converging  or 
diverging  rays. 

Rays  emanating  from  an  illuminating  or  an 
illuminated  point  always  diverge;  in  nature  there 
are  no  converging  rays,  neither  are  there  any 
absolutely  parallel,  but  those  proceeding  from  a 
point  twenty  feet  or  farther  away  are  so  nearly 
so  that  the  difference  can  only  be  mathematically 
expressed,  and  for  the  purposes  of  optics  are  con- 
sidered as  parallel.  According  to  the  calculations 
of  astronomers,  light  moves  at  the  rate  of  about 
186,000  miles  in  a  second;    according  to  this,  it 


94  LEWIS  POCKET 

requires  about  nine  minutes  for  the  waves  of 
light  from  the  sun  to  reach  the  earth,  and  those 
from  the  nearest  fixed  star  are  five  years  on  their 
journey  before  they  reach  us. 

From  an  optical  standpoint  we  now  refer  to  the 
"Wave  Theory,"  and  in  order  to  do  this  it  will 
be  necessary  to  draw  somewhat  on  one's  imagina- 
tion. You  have  ofttimes  noticed  when  a  stone 
is  dropped  into  a  calm  pond  of  water,  it  throws 
forth  circular  waves  in  all  directions.  The  first 
or  nearest  wave  to  the  stone  will  have  the  short- 
est radius  of  curvature,  or  in  other  words,  the 
greatest  strength  of  curvature.  As  this  wave 
spreads  it  will  decrease  in  curvature  until  it  has 
traveled  twenty  feet.  Beyond  20  feet  the  waves 
are  considered  plane, meaning  by  this  that,  when  on 
account  of  the  pupil  of  the  eye  being  about  an 
eighth  of  an  inch  in  diameter,  we  cut  from  a 
wave  of  light  that  has  traveled  twenty  feet  a 
piece  one-eighth  of  an  inch  long,  that  is,  the 
amount  that  would  enter  the  eye,  it  would  have 
so  slight  a  curve  that  it  is  considered  to  have 
none.     This  is  known  as  a  plane  wave. 

The  word  minus  denotes  less;  the  farther  the 
wave  travels  from  its  center  the  less  its  curva- 
ture, therefore  all  waves  that  are  going  from  a 
point  we  consider  minus,  and  for  the  sake  of 
simplicity  we  must  compare  the  waves  of  light 
with  the  waves  of  water,  and  instead  of  drop- 
ping the  stone  we  will  light  a  candle  that  will 
throw  off  waves  in  all  directions.  When  a  wave 
has  traveled  one-half  inch  from  a  point  it  has 
a  curve  of  minus  80,  because  it  has  a  radius  of 
curvature  of  eo  metre.  Now,  as  the  one  and 
same  wave  moves  on,  it  loses  its  curvature;  thus 


OPTICAL  DICTIONARY^  95 

when  it  has  traveled  one  inch  from  its  center  its 
curvature  is  less,  or  — 40,  and  at  two  inches, 
— 20;  three  inches,  — 13;  four  inches,  — 10;  five 
inches,  — 8;  twenty  inches,  — 2;  forty  inches, 
— 1;  eighty  inches,  — .50  (these  figures  are  the 
fractional  parts  of  a  metre,  which  the  distance 
represents) ;  twenty  feet,  no  curve,  or  plane  wave. 
"Now,  if  one  will  stop  to  think,  he  will  observe 
these  figures  compare  with  the  focal  length  of 
.lenses  in  the  trial  case;  that  is  to  say,  a  wave 
that  has  traveled  forty  inches  from  a  point  is 
known  as  a  — 1,  and  a  1-D.  lens  has  a  focal  length 
of  forty  inches.  A  wave  that  has  traveled  twenty 
inches  from  a  point  is  known  as  a  — 2,  while  a 
2-D.  lens  would  focus  at  twenty  inches.  For 
instance,  you  may  ask  yourself, ''What  would  be 
the  curvature  of  a  wave  of  light  that  has  a  radius 
of  thirteen  inches?"  You  would  at  once  think  of 
the  dioptric  number  of  the  lens  that  would  focus 
at  thirteen  inches.  This  would  be  a  3-D.  Then 
you  would  say  that  the  curve  is  — 3  if  it  is 
going  from,  a  point,  but  if  going  to  a  point,  +  3. 
You  will  notice  that  in  referring  to  a  metre 
it  is  spoken  of  as  forty  inches.  There  is  a  differ- 
ence between  the  two,  yet  it  is  near  enough  for 
our  purpose,  and  saves  the  trouble  and  incon- 
venience of  working  with  fractions;  so  far,  we 
have  spoken  of  the  minus  wave,  as  all  waves  in 
nature  are  minus;  in  order  to  have  a  plus  wave 
we  must  use  artificial  means,  and  will  work  out 
the  following  example:  Place  a  lighted  candle 
forty  inches  from  a  plus  3  sphere;  considering 
the  candle  the  point  from  which  the  light  comes, 
the  wave  has  traveled  from  a  point  forty  inches 
before  it  enters  the  lens,  therefore  it  enters  a 


96  LEWIS  POCKET 

minus  1  wave.  Minus  and  plus  neutralize. 
If  more  plus  than  minus  is  present  there  will 
remain,  after  neutralization,  an  amount  of  plus 
equivalent  to  the  difference.  Therefore  the 
minus  1  will  go  through  the  plus  3  sphere,  and 
will  emerge  a  plus  2  wave,  and  focus  at  twenty 
inches;  at  the  focus  they  will  cross  and  begin 
to  diverge,  or  rather  become  minus. 

Light  travels  at  the  rate  of  186,000  miles  in  a 
second  while  in  air,  but  in  passing  through  a 
denser  media,  such  as  glass,  its  speed  is  retarded, 
and  it  regains  its  former  speed  on  emerging  into 
air  again. 

It  always  depends  on  how  far  a  wave  is  from 
its  center  of  curvature  what  amount  of  curve  it 
will  have.     Study  the  following  examples: 


3^ 


.o^- 


%'^ 


D 

i 


i- 


/ 
/ 


-^ 


.CP 


ttOQ 

I- 

?  O 


Si 


.^ 


A. 


^•^ 


o 


o 


SB 

go* 

si 

^& 

BS 

is 

§5* 


§1- 

(DP* 


o 


•s 


JO 


tB  i::^j^  ^ 

p  o  ^  ^  ^  Q  ^P" 

§-§3cL^-h8 

,     ca3  "'  a  (D  *^  ^„ 


S  o  1^  ^trg  a-i2 

S  erg  so  P  B^P  S^ 
|w  ?;-clJ?  p-«>  p 


«     2  S  2  P  ^-tj 


§8:3  CD? 
P25 


*  ^  cf-2  r^p'p  "* 

rrsl  ^  '^  2  <P  C    I 


102  LEWIS  POCKET 

lAsht  Area  on  the  Face.  The  term  used  to  desig- 
nate the  Hght  upon  the  face  when  the  beam  of 
hght  from  the  retinoscope  is  directed  upon  the 
eye   under   observation. 

Light  Area  in  Pupil.  The  Hght  seen  in  the  pupil 
of  an  eye  under  observation  with  the  retinoscope, 
caused  by  the  reflex  from  the  retina.  Its  char- 
acter and  relative  movement  indicate  the  re- 
fractive condition  of  the  eye. 

Limbus  Cornea  (lim'-bus).  (Border  line.)  The 
region  where  the  cornea  and  sclerotic  join. 

Limit  Angle.     (See  Critical  Angle.) 

Limitans  (lim'-it-ans) .  That  which  limits  or  bounds 
a  body  or  organ. 

Line  of  Fixation.  A  line  which  connects  the  object 
looked  at  with  the  macula  lutea  through  the 
nodal  point  of  the  eye. 

Line  of  Vision.  The  line  which  connects  the  ob- 
ject looked  at  with  the  fovea  centralis  (visual 
axis) . 

Lippitudo  (lip-pi-tu'-do) .  An  inflammation  of  the 
margins  of  the  eyelids. 

V  Liquor  Morgagni.     A  small  quantity  of  fluid  between 
the  lens  and  its  capsule. 

Logadectomy  (log-ad-ek'-to-my).  A  removal  of  a 
part  of  the  conjunctiva  by  means  of  a  sharp  knife. 

Logades  (log'-ad-ees) .  The  first  coat  or  tunic  of  the 
eye. 

Loimophthal^mia.     Contagious  ophthalmia. 


OPTICAL  DICTIONARY.     .  103 

Long-Sightedness.     (See  Hyperopia.) 

Lorgnette  (lorn-yetO-  Double  eye-glasses  attached 
to  a  handle.  This  term  is  often  applied  to  opera- 
glasses. 

Louchettes.  A  kind  of  opaque  glasses  in  which,  for 
each  eye,  there  is  a  small  opening  which  makes 
it  impossible  to  look  in  any  other  way  than 
through  this  opening. 

Loxophthalmos  (lok-sof '-thal-mus) .  That  condi- 
tion in  which  the  eye  is  turned  from  parallelism. 
(Strasbismus;    Heterotropia.) 

Lucifugal  (lu-sif '-u-gal) .  That  condition  which 
exists  where  a  person  avoids  bright  light. 

Luminous  Bodies.  Those  sources  of  direct  light, 
as  the  sun,  a  lighted  candle,  etc. 

Luminous  Pupil.  The  appearance  of  the  pupil 
under  observation  with  the  retinoscope. 

S^  Luxation   (luk-sa'-shun)   of    Lens.     That  condition 
where  the  crystalline  lens  is  dislocated. 


iMacropsia  (mak-rop'-si-ah).  That  condition  of  an 
eye  in  which  objects  appear  larger  than  they 
really  are. 

Macroscopic  (mak-ro-scop'-ic).  That  which  may 
be  seen  with  the  naked  eye. 

Macula  Lutea  (mak'-yu-lah  lew'-te-ah).    Also  known 
y    as  che  yellow  spot  or  most  sensitive  spot  of  the 
retina,  situated  on  the  temple  side. 


104  LEWIS  POCKET 

Madarosis  (mad-ur-o'-sis).    That  condition  in  which 
the  eyelashes  are  permanently  destroyed. 


Maddox  Rod. 

Maddox  Rod.  An  opaque  disc  with  a  slit  through 
the  center.  Over  this  slit  is  placed  a  glass  rod  or 
cylinder.  In  looking  through  this  rod  at  a  small 
round  light,  it  causes  the  light  to  look  like  a  long 
streak.  This  rod  is  used  for  testing  muscular 
insufficiency.  Before  testing  for  muscular  im- 
balance correct  all  errors  of  refraction. 

Madisterium  (mad-is-ter'-i-um) .  An  instrument 
used  for  removing  the  eyelashes. 

Magnet  Operation.  A  method  used  for  removing 
particles  of  iron  and  steel  embedded  within  the 
tissues  of  the  eye,  by  means  of  a  magnet. 

Magnify  (mag'-ni-f y) .  To  render  an  apparent  in- 
crease in  the  size  of  an  object. 

Malacia  (mal-a'-se-ah) .     Morbid  softening  of  tissue. 


OPTICAL  DICTIONARY.  105 

Malacocataracta  (mal-ak-o-kat-ar-ak'-tah).  A  soft 
cataract  which  forms  in  the  c.ystaUine  lens  of  a 
person  under  the  fortieth  year.  This  form  of 
cataract  is  usually  the  result  of  injury. 

Malaxation  (mal-ax-a'-shun).  A  rubbing  or  knead- 
ing of  the  eyeball. 

Malignant  (mal-ig'-nant).     Fatal. 

Malingerer.     One  who  pretends  to  have  a  defect  of- 
vision  or  some  other  function  to  evade  duty. 

Marginal  Keratitis  (mar'-jin-al  ker-at-i'-tis) .  A  dis- 
ease of  an  inflammatory  nature  which  occurs 
usually  in  elderly  people.  The  inflammation  ex- 
tends around  the  rim  of  the  cornea.  If  the 
process  continues  the  cornea  is  invaded  by  a 
densely  vascular,  superiicially  ulcerated,  and 
yet  thickened  zone. 

Marmarygea  (mar-mar'-ij-e-a).  Appearance  of 
sparks  before  the  eyes. 

Mature  (ma-tur').     Fully  developed;   ripe. 

Media.  The  refracting  humors  of  the  eye.  Opti- 
cally, media  is  the  plural  of  medium. 

Medium.  Intervening  body  or  quantity.  The  diop- 
tric media  of  the  eye  consist  of  the  cornea,  aque- 
ous humor,  crystalline  lens,  and  vitreous  humor. 

Megalocornea  (meg-al-o-kor'-ne-ah) .  That  condi- 
tion in  which  there  is  bulging  of  the  cornea. 

Megalopia  (meg-al-o'-pi-ah).     (See  Macropsia.) 


106 


LEWIS  POCKET 


Megalopsia  (meg-al-op'-si-ah) .  That  condition  of 
the  eye  in  which  objects  appear  larger  than  they 
really  are. 

Meg'aloscope.     A  large  magnifying  lens. 

Megascope  (meg'-a-skope) .  A  microscope  for  ex- 
amining large  objects. 

Megophthalmus  (meg-of-thar-mus) .  That  condi- 
tion in  which  the  eye  is  abnormally  large. 


ANATOMY  OP  LIDB. 


No.  1.  Melhomian  Glands.  No.  5. 
No.  2.  Puncta  Lachrymalia.  No.  6. 
Nos.  3  and  4.    Lachrymal  Oanals. 


Orbicularis  Muscles. 
Lachrymal  Glands, 


Meibomian  Glands  (mi-bo'-me-an).  A  variety  of 
\r  glands  which  are  embedded  in  the  tarsal  cartilages. 
There  are  from  thirty  to  forty  in  the  upper  lid  and 
from  twenty  to  thirty  in  the  lower  lid.  Their  ducts 
open  upon  the  free  margin  of  the  lids.  These 
glands  secrete  a  sebaceous,  oily  fluid  which  assists 
in  lubricating  the  lids  as  they  glide  over  the  eyeball, 
and  also  prevents  the  lids  from  sticking  together 
when  we  have  them  closed,  ^  Another  function  is, 


V 


OPTICAL  DICTIONARY.  107 

that  as  the  margins  of  the  lids  are  kept  oily  at 
all  times  the  tears  do  not  flow  over  them  so  easily. 
This  oily  substance  also  mixes  with  the  tears  and 
assists  in  preventing  friction  between  the  eyeball 
and  lids,  and  at  the  same  time  prevents  the  cornea 
from  becoming  dry  so  quickly. 

Mel'anin.  A  dark  pigment  from  choroid,  hair,  and 
other  dark  tissues. 

Melasma  Palpebrarum  (mel-as'-ma  pal-pe-bra'-rum) . 
A  discoloration  of  the  eyelid,  which  occurs  fre- 
quently in  pregnant  women. 

Membrana  Capsularis.  That  portion  of  the  arteria 
centralis,  which  forms  a  vascular  network  and 
coats  the  posterior  surface  of  the  lens. 

Membrana  Pupillaris  (mem-bra'-na) .  A  membrane 
covering  the  pupil  in  fetal  life.  This  sometimes 
fails  to  disappear. 

Membrane  (mem'-bran).  A  thin  tissue  covering 
some  surface  or  organ. 

Membrane  Nictitating.  That  which  is  sometimes 
called  the  third  eyelid,  to  be  seen  in  various 
animals. 

Meniscus  Glasses  (men-is'-kus) .  (Or  Periscopic.) 
Glasses  that  refract  at  some  distance  from  the 
center  the  same  as  at  the  center,  so  that  one  can 
see  obliquely  through  them.  Minus  on  one  side 
and  convex  on  the  other.      Convexo  concave. 

Menotyphlosis  (men-o-tyf-lo'-sis) .  A  condition  of 
the  eye  in  which  tr^re  is  diminution  of  vision 
during  night. 


i08  LEWIS  POCKET 

Mcramaurosis  (mer-am-au-ro'-sis) .  A  condition  of 
the  eye  in  which  part  of  the  field  of  vision  is  lost; 
partial  amaurosis. 

Meridian  (mer-id'-i-an) .  A  meridian  of  a  circle  is 
any  one  of  its  several  diameters.  A  meridian  of 
a  lens  is  any  line  crossing  its  surface  over  its 
optical  center.  A  meridian  of  the  cornea  is  any 
line  crossing  its  surface  through  its  anterior  pole. 
A  circle  describes  360  degrees,  one-half  of  which, 
or  180  degrees,  is  marked  on  trial  frame.  0  and 
180  are  generally  found  in  the  horizontal,  90 
describes  the  vertical.  On  the  clock-dial  they 
are  numbered  from  left  to  right,  and  on  trial 
frame  from  the  right  to  the  left.  The  figures 
on  trial  frame  correspond  with  clock-dial  when 
they  are  face  to  face. 

Meropia  (mer-o'-pi-ah).     (See  Amblyopia.) 

Mesoropter  (mes-o-rop'-ter).  The  position  of  eyes 
in  state  of  absolute  rest. 

Metamorphopsia  (met-am-or-fop'-si-ah).  That  con- 
dition of  the  eye  in  which  objects  appear  distorted. 

Vi  Meter  Angle.  An  angle  formed  by  the  visual  axes 
of  the  two  eyes  looking  at  a  point  one  metre 
distant. 

Metre  Lens.  A  lens  that  will  focus  parallel  rays  at 
a  distance  of  one  metre. 

Metric  Curve.     A  curve  that  has  a  radius  of  one 

metre. 

Microblepharia  (mi-kro-blef-a'-ri-ah).  A  very  nar- 
row and  thin  eyelid. 


OPTICAL  DICTIONARY  109 

Microcornia  (mi-kro-kor'-ne-ah) .     A   small   cornea. 

Microlentia  (mi-kro-len'-ti-ah) .  A  very  small  crys- 
talline lens. 

Micrometer.  An  instrument  which  is  used  for  mak- 
ing measurements  of  very  small  bodies. 

Micropsia  (my-krop'  see-ah).  That  condition  of 
the  eye  in  which  objects  appear  smaller  than  they 
really  are. 

Microphthalmia  (my-krof-thal'-mee-ah) .  Abnor- 
mally small  eyes. 

Microscope  (mi'-kro-scope).  An  optical  instrument 
used  for  examing  minute  objects. 

Milium.  A  small  elevation,  on  the  skin  of'  the  eye- 
lid, filled  with  a  greasy  secretion. 

Milphae  (mil'-phae).  A  morbid  condition  in  which 
the  eyelashes  drop  out. 

Milphosis  (mil-fo'-sis).  That  condition  in  which  the 
eyebrows  as  well  as  the  eyelashes  have  fallen  out. 

Minus.     Minus  lenses,  same  as  concave. 

V  Miosis    (mi-o'-sis).     Excessive    contraction    of    the 
pupil. 

Miotic  (mi-otMc).  Any  agent  or  medicine  which 
causes  the  pupil  to  contract. 

Mirror.  An  instrument  of  regular  reflection,  thus 
capable  of  creating  images. 

Monoblepsia  (mon-o-blep'-si-ah).  Blindness  to  all 
colors  but  one. 


no  LEWIS  POCKET 

Monocle  (mon'-o-kl).  A  large  round  glass  worn 
within  the  socket  of  either  eye. 

Monocular  (mon-ok'-u-lar).  Having  one  eye  only. 
Monocular  vision  is  that  condition  where  the 
patient  has  vision  in  one  eye  only. 

Moon-Blindness.  Amblyopia  caused  by  having  the 
eyes  exposed  to  the  full  glare  of  the  moon  for 
considerable  time. 

Monops  (mon'-ops).     A  foetus  with   but  one  eye. 

Motor.  A  nerve  center  controlling  motion.  A 
muscle  causing  motion. 

Motor  Muscles.  The  muscles  that  control  the 
movements  of,  or  parts  of,  the  eyes — the  recti, 
the  oblique  muscles,  the  ciliary,  and  the  iris 
muscles. 

Mucocele  (mu'-ko-sele).  Distention  of  the  lachry- 
mal sac,  chronic  thickening  of  the  Hning  mem- 
brane, and  increased  secretion  of  mucus.  The 
mucus  may  be  clear  or  turbid.  Any  tumor  con- 
taining mucus. 

\  Muscae  Volitantes  (mus'-cae  vol-i-tan'-tes) .  Small 
Y  floating  bodies,  resembling  sticks,  etc.,  which 
niove  about  in  the  field  of  vision,  but  do  not  ac- 
tually cross  the  fixation  point,  and  never  inter- 
fere with  sight.  They  are  usually  seen  against 
some  bright  object.  They  depend  upon  minute 
changes  in  the  vitreous,  which  are  present  in 
nearly  all  eyes.  They  vary,  or  seem  to  vary, 
greatly  with  the  health  and  state  of  the  circula- 
tion, but  are  of  no  real  importance.  They  are 
most  abundant  and  troublesome  in  myopic  eyes. 


OPTICAL  DICTIONARY.  Ul 

tyiUBcles  (Eye;.     There  are  six  extrinsic  muscles  tnat 
\     move  the  eyeball,  namely: 

Internal  Rectus  Muscle  turns  the  eye  in, 
and  is  supplied  by  the  third  cranial  or  motor 
oculi  nerve. 

Superior  Rectus  Muscle  turns  the  eye  up, 
and  is  supplied  by  the  third  cranial  or  motor 
oculi  nerve. 

Inferior  Rectus  Muscle  turns  the  eye  down, 
and  is  supplied  by  the  third  cranial  or  motor 
oculi  nerve. 

Inferior  Oblique  Muscle  rolls  the  eye  on  its 
optic  axis,  drawing  the  bottom  and  back  part  of 
the  eye  in  and  down  while  the  front  moves  up  and 
out,  and  is  supplied  by  the  third  cranial  or  motor 
oculi  nerve. 

External  Rectus  Muscle  turns  the  eye  out, 
and  is  supplied  by  the  sixth  cranial  or  abducens 
nerve. 

Superior  Oblique  Muscle  rolls  the  eye  on  its 
optic  axis,  turning  the  back  part  of  the  eye  in- 
ward and  upward,  while  the  front  part  moves 
down  and  out,  and  is  supplied  by  the  fourth 
cranial  or  patheticus  nerve. 

The  ciUary  muscles  are  inside  the  eyeballs,  and 
are  used  for  accommodating  only.  They  are 
supplied  by  the  third  nerve. 

Th«  orbicularis  palpebrarum  muscle  closes  the 
lids,  and  is  supplied  by  the  seventh,  or  facial 
nerve.     (One  of  the  muscles  of  expression.) 

The  levator  palpebra  superioris  lifts  the  lids, 
and  is  fed  by  a  branch  of  the  third  cranial  nerve. 

The  sphincter  muscle  which  closes  the  pupil  is 
supplied  by  the  third  nerve. 


112 


LEWIS  POCKET 


The  radiating  muscles  of  the  iris  which  dilate 
the  pupil  are  supplied  by  the  sympathetic  nerve. 


Tensor  tarsi  compresses  the  lachrymal  sac  and 
pulls  the  puncta  against  the  eyeball.  Supplied 
by  the  seventh  cranial  nerve. 


OPTICAL  DICTIONARY. 


113 


Corrugator  supercilii  draws  eyebrow  down  and 
inward,  and  is  supplied  by  the  seventh  facial 
nerve. 

Pyramidalis  nasi.  This  muscle  depresses  the 
eyebrow.     Supplied  by  the  seventh  facial  nerve. 


Cut  showing  the  Extrinsic  Muscle. 


114  LEWIS  POCKET 

Muscular  Asthenopia.     (See  Asthenopia.) 

Muscular  Imbalance.  It  is  generally  agreed  by  the 
authorities  of  today  that  ametropia  is  responsible 
for  90  per  cent  of  Muscular  Imbalance.  For  this 
reason  it  is  considered  advisable  to  always  correct 
any  ametropia  that  may  be  present,  and  have  the 
patient  wear  the  correction  for  at  least  six  weeks. 
At  the  end  of  this  time,  should  any  muscular  im- 
balance be  manifest,  correct  half  of  the  amount. 
Always  test  for  muscle  trouble  while  the  patient 
is  wearing  his  full  correction  for  the  ametropia, 
otherwise  it  will  not  be  considered  a  proper  test. 
There  are  but  few  exceptions  to  this  rule;  e.  g., 
when  a  prism  base  in,  will  allow  you  to  decrease  a 
minus  lens  or  increase  a  plus,  prescribe  it. 

Mycophthalmia  (me-kof-thal'-mi-ah) .  Inflammation 
of  the  conjunctiva,  caused   by  a  spongy  growth. 

Mydriasis  (mid-ri'-as-is).  Dilatation  of  the  pupil, 
caused  by  the  use  of  atropine  or  other  mydriatics, 
or  paralysis  of  the  motor  oculi  nerve. 

Mydriatic  (mid-ri-at'-ic).  A  drug  that  dilates  the 
pupil. 

Myiocephalon  (my-i-o-sef '-al-on) .  A  small  protru- 
sion of  the  iris  through  a  perforation  of  the  cornea. 

Myodesopsia.     (See  Muscae  Volitantes,) 

Myope  (my'-ope).     A  nearrsighted  person. 

\^  Myopia  (my-o'-pi-ah).  Same  as  brachymetropia  and 
hypometropia.  A  visual  defect  which  causes 
parallel  rays  of  light  to  focus  in  front  of  the  retina, 
with  the  muscles  of  accommodation  at  rest.     The! I 


OPTICAL  DICTIONARY.  115 

eyeball  may  be  too  long  (axial)  or  the  refraction 
too  great,  causing  the  parallel  rays  to  cross  and 
meet  the  retina  as  divergent  rays,  which  form  a 
circle  of  diffusion,  and  so  cause  a  blurred  and 
indistinct  image  of  the  object.  Myopia  from 
excess  of  curvature  is  much  rarer  than  the  axial 
form.  We  sometimes  see  a  case  of  apparent 
Myopia  due  to  excess  of  curvature  of  the  lens, 
caused  by  a  spasm  of  the  ciliary  muscle.  This 
is  what  is  known  as  false  myopia,  and  will  disap- 
pear under  the  influence  of  atropine. 


These  cuts  havejjnot  been  made'with  mathematical  precision,  but 
are  merely  intended  to  roughly  exemplify  the  principle  in- 
volved. The  above  illustrates  the  effect  of  a  distant  point 
upon  a  myopic  eye.  It  will  be  observed  that  the  rays  from 
the  distant  point  cause  the  image  from  that  point  to  spread 
out  over  a  considerable  area  on  the  retina.  A  million 
points  would  make  a  million  blurred  spots.  They  would 
overlap  each  other  and  render  the  picture  indistinct. 

Bonders  prcnounced  every  highly  myopic  eye 
a  diseased  eye,  but  of  late  years  it  has  been  shown 
that  this  remark  is  liable  to  convey  a  false  mean- 
ing. It  is  admitted  that  up  to  3-D.  the  cases  are 
seldom  serious,  it  being  generally  possible  to 
give  perfect  vision  by  proper  glasses,  but  when 
the  case  is  above  5-D.  we  do  not  expect  to  obtain 
perfect  vision  by  proper  lenses,  and  look  for  varl 
cus  pathological  conditions. 


116  LEWIS  POCKET 

Symptoms.  The  patient  sees  distant  objects 
badly  and  near  objects  well.  The  pupils  are 
usually  large,  and  as  presbyopia  advances 
they  contract.  The  eyes  look  prominent 
and  the  patient  complains  of  fatigue,  pain, 
and  intolerance  of  light.  All  of  these  symptoms 
will  pass  away  when  the  right  correction 
is  worn.  The  cili?iry  muscle  is  smaller  and 
weaker  than  in  the  normal  or  emmetropic  eye. 
As  a  rule  myopic  patients  cannot  wear  their 
full  correction  when  first  fitted,  but  after  wear- 
ing about  two-thirds  of  the  correction  for  about 
six  weeks  the  full  amount  may  be  prescribed. 
Myopia  that  is  gradually  on  the  increase  is  called 
Progressive  Myopia.  Myopia  that  is  of  a  rapidly 
progressive  type,  and  is  very  destructive  to  the 
tissues  of  the  eye,  is  called  Malignant  Myopia. 

r 

Myopic  Crescent.  As  seen  by  the  ophthalmoscope, 
is  a  white  crescent  at  the  outer  side  of  the  optic 
disc.  This  condition  is  caused  by  the  choroid 
being  torn  away  from  the  optic  disc  and  allowing 
the  sclerotic  to  show  through.  Found  in  high 
degrees  of  myopia. 

Myosis  (my-o'-sis).  Abnormal  contraction  of  the 
pupil.     (Same  as  miosis.) 

Myotic.  An  agent  that  will  contract  the  pupil,  such 
as  eserin,  pilocarpine,  etc. 

Myotomy  (mi-ot'-o-me) .  The  dissection  or  divi- 
sion of  muscles. 


OPTICAL  DICTIONARY.  117' 

IN  asal  Duct.  That  part  of  the  tear  duct  below 
lachrymal  sac,  and  opening  into  the  nose. 

\Near  Point  (or  Punctum  Proximum).  The  nearest 
^  point  at  which  the  eye  can  see  distinctly  when 
employing  its  full  amount  of  accommodation. 
It  varies  with  the  amount  of  accommodation  the 
eye  possesses.  The  way  to  determine  the  near 
point  is  to  note  the  shortest  distance  at  which 
an  emmetrope  can  read  small  print  with  each 
eye  separately.  Properly  speaking,  the  near 
point  is  that  point  for  which  the  ^eyes'  refraction 
is  adjusted  when  the  full  amount  of  accommoda- 
tion is  being  used. 

Near-Sight.     (See  Myopia.) 

Neb'ula.     Slight  corneal  opacity. 

Needling  (needMing).     An  operation  for  soft  cata- 
ract.   The  lens  capsule  is  needled,  and  the  aqueous 
^  allowed  to  absorb  the  lens. 

Negative  (neg'-a-tive) .  The  opposite  of  positive. 
The  negative  surface  of  a  periscopic  lens  is  the 
concave  surface. 

Neotocophthalmia  (ne-ot-ok-of-thal'-mi-ah) .  (See 
Ophthalmia  Neonatorum.) 

Nephablepsia  (nef-ab-lep'-si-ah).  (See  Snow-Blind- 
ness.) 

Nephelopia  (nef-el-o'-pi-ah) .  A  diminutior.  of  vision, 
caused  by  a  cloudiness  of  the  transparent  parts 
of  the  eye. 


118  LEWIS  POCKET 

Nephritic  Retinitis  (nee-f rif-ik) .  A  form  of  inflam- 
mation of  the  retina  associated  with  Bright's  dis- 
ease of  the  kidneys,  characterized  by  white 
streaks  along  the  course  of  the  blood-vessels. 

Nerve.  A  white  string-like  fiber  which  transmits 
impressions  from  an  organ  to  the  brain  or  from 
the  brain  to  an  organ.  Cranial  n.,  any  nerve 
arising  from  the  brain  direct.  There  are  twelve 
cranial  nerves,  as  follows: 

1.  Olfactory,  special  sense  of  smell. 

2.  Optic,  special  sense  of  sight 

3.  Motor  Oculi,  motor  nerve  for  eye  muscles. 

4.  Patheticus,  motor  nerve  for  superior  oblique 
muscle. 

5.  Trigeminus,  sensory,  motion,  and  taste. 

6.  Abducens,  motor  nerve  for  external  rectus 
muscle. 

7.  Facial,  motor  nerve  for  muscles  of  face. 

8.  Auditory,  special  sense  of  hearing. 

9.  Glosso-Pharyngeal,  sensation  and  taste. 

10.  Pneumogastric,  sensation  and  motion. 

11.  Spinal  Accessory,  motion. 

12.  Hypo  Glossal, 

Motor  n.,  one  which  contains  wholly  motor 
fibers.  N.  center,  a  group  of  cells  which  consist 
of  gray  matter  and  have  a  common  function. 
Mixed  n.,  a  nerve  which  is  both  motor  and  sensory. 
N.  head,  the  optic  disc  or  papilla.  Sensory  n., 
any  nerve  which  transmits  sensations  or  im- 
pulses. Sympathetic  n,,  any  nerve  of  the  sympa- 
thetic system. 

Nerve  (Optic).  The  nerve  that  transmits  retinal 
sensations  to  the  centers  of  perception  in  the 
brain,    there   to   be   translated   into   sight.     The 


View  of  the  Eye  from   the  Temporal  side 
with  part  of  the  Orbit  Removed. 

1.  Eyeball  with   part   of    external   rectus 

muscle. 

2.  Superior  Maxilla. 

3.  Third   pair  (or    Motor  Oculi)   nerves. 

They  are  distributed  to  all  the 
muscles  of  the  eye  except  the  Supe- 
rior Oblique,  External  Rectus  and 
the  Dilator  Muscles  of  the  Iris. 

4.  Fourth  pair  of  Nerves,  feeding  Superior 

Oblique  Muscles. 

6.     Sixth  pair  of  Nerves,  feeding  External 
Rectus. 

8.     Ciliary  Nerves  entering  the  globe. 


OPTICAL  DICTIONARY  119 

nervous  system  is  a  system  of  connection  and 
communication  by  which  the  different  organs, 
vessels,  and  various  parts  of  the  body  are  brought 
into  direct  relation  with  each  other  and  with  the 
mind,  and  the  various  organs  stimulated  to 
harmonious  or  alternating  action.  It  consists 
of  the  brain  and  spinal  cord,  called  the  central 
nervous  system,  which  controls  the  voluntary 
actions  of  the  body,  sometimes  called  the  nerves 
of  animal  life,  and  is  directly  connected  with  the 
sympathetic  nerves,  w^hich  have  been  termed 
nerves  of  organic  life,  they  being  involuntary 
nerves  and  control  the  involuntary  action  of  the 
various  vital  processes  of  the  body.  The  nervous 
system  is  divided  into  the  cerebro-spinal  or  cen- 
tral, sympathetic,  and  the  vaso  motor.  The 
vaso  motor  system  is  a  part  of  the  sympathetic 
system  and  consists  of  the  vaso  motor  center 
located  in  the  medulla  oblongata,  of  certain 
other  subsidiary  vaso  motor  centers  in  the 
spinal  cord,  and  of  vaso  motor  nerves.  This 
system  is  connected  with  the  blood-vessels  in 
the  various  parts  of  the  body,  the  muscular 
coats  of  which  are  supplied  with  filaments  and 
plexuses  of  vaso  motor  nerves  which  regulate 
the  size  of  the  blood-vessels.  They  are  of  two 
kinds:  vaso  dilators,  stimulation  of  w^hich  cause 
dilatation  of  the  blood-vessels  and  an  increased 
amount  of  blood  to  a  part,  and  vaso  constrictors, 
stimulation  of  which  cause  constriction  or  con- 
traction of  the  blood-vessels  and  a  diminished 
amount  of  blood  to  a  part.  This  last  named 
system  is  very  important  to  the  practitioners 
of  manipulatory  forms  of  healing,  and  has  nly 
in  the  past  few  years  been  known  to  any  extent, 


120  LEWIS  POCKET 

the  vaso  motor  center  being  discovered  by 
Schiff  in  1855,  and  more  accurately  localized 
by  Ludwig  in  1871.  The  cranial  nerves  are 
those  that  have  their  apparent  origin  in  the 
cranium.  Sommering  and  other  European 
anatomists  name  twelve  pairs,  while  WilHs  and 
a  few  other  authors  designate  only  nine  pairs, 
according  to  the  order  in  which  they  pass  out 
of  the  base  of  the  brain. 

Neuritis    (neu-ri'-tis) .     Inflammation   of   the    optic 
nerve. 

Neurology  (nu-rol'-o-je) .     A  study  of  the  nervous 
system. 

Neurodealgia.     Pain  or  excessive  sensibility  of  the 
retina. 

Neurodeatrophia.     Atrophy  of  the  retina. 

Neuroretinitis    (neu-ro-ret-in-i'-tis) .      Inflammation 
of  the  optic  nerve  and  retina. 

Neutralize  (neu'-tral-ize).  The  method  of  counter- 
balancing or  doing  away  with  power  in  lenses. 
In  order  to  det  rmine  whether  a  lens  is  of  plus 
or  minus  power,  hold  it  up  and  look  at  some  dis- 
tant object  through  it,  then  move  the  lens  from 
side  to  side  and  if  the  object  appears  to  move 
in  the  opposite  direction  to  the  movement  of  the 
lens  it  is  a  plus  lens.  If  you  wish  to  find  its 
dioptric  power,  take  from  your  trial  case  a  minus 
lens  and  put  them  together  and  again  look 
through  them  at  the  object,  and  should  the  object 
still  move  against  the  movement  of  the  lenses  the 
minus  is  not  strong  enough.  On  the  other  hand, 
should  the  movement  be   reversed   and  now  the 


OPTICAL  DICTIONARY.  Ul 

objects  appear  to  move  with  the  lenses  the  minus 
is  too  strong,  and  you  must  find  the  minus  lens 
that  will  allow  the  object  to  remain  stationary. 
Whatever  minus  lens  is  required  to  do  this  will 
be  of  the  same  power  as  your  plus  lens;  for  in- 
stance, it  will  require  a  — 3  sphere  to  neutralize 
a  +3  sphere.  When  you  look  at  an  object 
through  a  minus  lens,  and  move  the  lens  as 
explained  above,  the  object  will  appear  to  move 
with  the  movement  of  your  lens,  and  in  order 
to  find  its  dioptric  power  use  plus  lenses  as  in 
the  previous  test  until  all  movement  of  the 
object  looked  at  has  disappeared,  and  then  the 
minus  lens  will  be  the  same  power  as  your  plus. 
If  the  lens  is  compound,  use  the  weakest  spherical 
lens  which  neutralizes  the  motion  in  one  direc- 
tion; this  usually  gives  the  spherical  surface, 
then  use  a  cylinder  to  neutralize  motion  at  right 
angles  to  this.  If  in  order  to  neutralize  a  given 
compound  lens,  -f2  sphere  combined  with  +1 
cylinder,  axis  90*'  is  required,  then  the  lens  being 
neutralized  is  a  — 2  sphere  combined  with  — 1 
cylinder,  axis  90^,  etc. 

Nictitation  (nik-tit-a'-shun) .  Involuntary  convul- 
sive twitching  of  the  eyelids. 

Xight-Blindness.     (See  Hemeralopia.) 

Niphablepsia  (nif-ab-lep'-si-ah) .  That  condition 
wherein  blindness  is  caused  by  the  glaring  reflec- 
tion of  sunlight  upon  the  snow.     Snow-blindness. 

No'dal  Points.  (Or  Cardinal  Points.)  Are  two  points 
situated  on  the  optic  axis,  connecting  the  centers 
of  curvature  of  the  refracting  compound  dioptric 


system  of  the  eye.  The  nodal  points  of  the  eyo 
are  so  close  together  that  they  may  be  considered 
as  one  point.* 

Normal.  That  which  conforms  to  the  natural  rule. 
A  straight  line  drawn  from  any  point  of  a  curve 
or  surface  so  as  to  be  perpendicular  to  the  curve 
or  surface  at  the  point  which  it  strikes  is  said 
to  be  normal  to  the  surface. 

Normal  Vision.  Vision  is  said  to  be  normal  when 
an  eye  can  read  a  line  on  Snellen's  Test  Type 
from  the  distance  at  which  it  is  numbered. 
The  smaller  the  objects  that  an  eye  can  dis- 
tinguish or  the  greater  the  distance  at  which  it 
can  distinguish  an  object  of  given  size,  the  greater 
is  the  acuity  of  vision  that  it  possesses.  Sup- 
pose, for  instance,  that  the  eye  is  just  able  to 
distinguish  the  letters  in  the  line  marked  50  on 
the  Snellen's  test  type  from  a  distance  of  twenty 
feet,  then  the  vision  would  be  20/50.  The  vision 
in  this  case  would  not  be  as  good  as  if  the  line 
marked  40  had  been  read  from  the  same  distance; 
and  in  order  to  have  normal  vision  the  patient 
should  read  the  line  marked  20  at  twenty 
feet,  with  each  eye  separately,  then  the  vision 
would  be  known  as  20/20.  Sometimes  the 
patient  will  read  the  line  marked  15  or  even  10 
from  twenty  feet.  In  this  case  the  vision  is 
exceptionally  acute,  and  is  designated  as  20/  15 
or  20/10. 

Normal  vision  does  not  indicate  that  the  eye 
is  normal,  as  the   patient   may  be   straining  to 
bring  the  vision  up  to  this  point,  as  in  Faculta- 
tive  Hypermetropia.     Again,   an   emmetropic   eye 
does  not  always  have  normal  vision. 


V 


Nubecula  (nu-bek'-u-la) .  "Slight  cloudiness  of  the 
cornea. 

Nuclear  Cataract.     (See  Cataract.) 

Nyctalopia  (nyk-tal-o'-pi-ah) .     (See  Day-Blindness.) 

Nyctotyphlosis  (nyk-to-tyf-lo'-sis) .  State  of  blind- 
ness at  night-time. 

Nystagmus  (nys-tag'-mus) .  Short,  jerking  move- 
ments of  the  eye  which  are  very  rapidly  repeated 
and  always  occur  in  the  same  direction.  The 
movements  of  the  eye,  as  a  whole,  are  not  affected 
by  it.  Defective  vision  of  such  cases  is  not  to  be 
attributed  to  the  nystagmus,  but,  on  the  con- 
trarj^,  is  the  cause  of  it.  Vertical  n.,  the  eyes 
continually  move  vertically.  Lateral  n.,  the  eyes 
constantly  move  horizontally.  Rotary  n.,  the 
eyes  constantly  rotate. 


Ubfuscation  (ob-f us-ka'-shun) .  An  obscuration 
of  vision  or  a  confusion  of  sight. 

Object.  Something  visible  or  tangible.  That  which 
is  seen.  An  external  something  the  image  of 
which  is  upon  the  retina,  which  is  intelligently 
impressed  and  appreciated  by  the  brain. 

Objective  (ob-jek'-tive).  Symptoms  observed  by 
operator  usually  with  ophthalmoscope  or  retino- 
scope.  Symptoms  which  the  refractionist  dis- 
covers by  means  Oi  one  or  more  of  his  five  senses; 
Objective  Examination.  An  examination  cou' 
ducted  independent  of  the  patient's  statements. 
6.  g.^  retinoscopy. 


124  LEWIS  POCKET 

Oblique.  '  Slanting;  placed  in  a  plane  between  the 
horizontal  and  vertical  planes. 

Occlusion  of  the  Pupil  (ok-klew'-zhun).  Blocking 
up  of  the  pupil  by  a  membrane. 

Ocular  (ok-'u-lar).     That  which  pertains  to  the  eye^ 

Ocular  Refraction.  The  science  treating  of  the 
optical  conditions  of  the  eye,  the  estimation  of 
its  errors  of  refraction  and  their  connection  with 
lenses  for  the  eye. 

Ocular  Spectres.  Imaginary  objects  floating  before 
the  eyes. 

Oculist  (ok'-u-list) .  A  physician  and  surgeon  who 
has  received  the  degree,  **  Doctor  of  Medicine,"  and 
makes  a  speciality  of  the  eye  and  its  diseases. 

Oculomotor  (ok'-yu-loh-moh'-tor).  Pertaining  to 
the  movements  of  the  eye. 

Oculus  (ok'-yu-lus) .     The  organ  of  vision. 

O.  D.     Oculus  Dexter.     The  right  eye. 

Offset  Guard.  An  eye-glass  guard  with  a  long 
shank,  the  purpose  of  which  is  to  hold  lenses 
farther  from  the  eyes. 

Old  Sight.     (See  Presbyopia.) 

O'nyx.  An  accumulation  of  pus  between  the  layers 
of  the  cornea. 

Opacity  (o-pas'-i-ty).     A  want  of  transparency. 

Opaque  (o-pake').  Impervious  to  light.  Not  trans- 
parent. 


OPTICAL  DICTIONARY.  125 

Operculum  Oculi  (o-per-cu'-lum  oc'-u-li).  The  eye- 
lid. 

Operation  (op-er-a'-shun) .  An  act  performed  with 
instruments  or  by  the  hands  of  a  surgeon. 

Ophryitis  (of-ry-i'-tis).  That  condition  in  which  the 
eyebrows  are  inflamed. 

Ophrys  (of'-rys).     Eyebrows. 

Ophthalmagra  (of-thal'-ma-grah) .  A  sudden  intense 
pain  in  the  eye,  usually  rheumatic  or  gouty  in 
origin. 

Ophthalmalgia  (of-thal-mal'-ge-ah) .  Sudden  vio- 
lent pain  in  the  eye,  not  the  result  of  inflamma- 
tion, but  neuralgic  in  character. 

Ophthalmatrophia  (of-thal-mah-tro'-fe-ah).  Atrophy 
of  the  eye. 

Ophthalmia  (of-thal'-mi-ah).  Severe  inflammation 
of  the  eye.  This  more  particularly  applies  to 
the  conjunctiva  of  the  eyelids  and  eyeball. 

Ophthalmic  (of-thar-mic) .  That  which  pertains  to 
the  eye. 

Ophthalmitic  (of-thai-mit'-ic) .  That  which  applies 
to  inflammatory  diseases  of  the  deeper  as  well  as 
the  superficial  structures  of  the  eye. 

Ophthalmitis  (of-thal-mi'-tis) .  Inflammation  of  the 
eye,  more  especially  the  globe  with  its  membranes. 

Ophthalmoblennorrhoea  (-blen-ur-ree'-ah).  A  flow  of 
mucus  from  the  eye. 

Ophthalmocarcinoma  (-kahr-si-no'-mah).  Cai^cer 
of  the  eye. 


126  LEWIS  POCKET 

Ophthalmocele.       (See  Stapyloma.) 

Ophthalmocopia  (-koh'-pee-ah) .  Fatigue  of  the  eyes; 
Asthenopia.  * 

Ophthalmodynia  (-din'-e-ah) .  Neuralgic  pain  of  the 
eye. 

Ophthalmography  (-mog'-rha-f ee) .     A  description  of 

the  eye. 

Ophthalmologist  (of-thal-moF-o-gist) .  One  who 
practices  opthalmology  and  has  taken  the  degree, 
^'Doctor  of  Medicine."     An  Oculist. 

Ophthalmology  (of-thal-mol'-o-gy) .  A  study  of  the 
eye  and  its  diseases. 

Ophthalmomiaerosis  (-ma-kro'-sis) .  Enlargement  of 
the  eyeballs. 

Ophthalmomalacia  (-ma-la'-sha) .  That  condition  in 
which  there  is  abnormal  softness  of  the  eyeball. 

Ophthalmopathy  (-mop'-a-thee) .  Any  disease  of  the 
eye. 

Ophthalmophthisis  (-mof '-thi-sis) .  That  condition 
in  which  there  is  wasting  of  the  eyeballs. 

Ophthalmoplegia  (-ple'-jah).  Paralysis  of  the 
ocular  muscles  of  the  eye.  O.  Partial,  a  form 
In  which  only  some  of  the  muscles  are  para- 
lyzed. O.  Progressive,  a  gradual  paralysis  of  all 
the  muscles  of  both  eyes.  O.  Total,  when  the 
iris  and  ciliary  body,  as  well  as  the  external 
muscles,  are  paralyzed.  O.  Externa,  when  the 
external  muscles  are  paralyzed.  O.  Interna,  par- 
alysis of  the  internal  muscles. 


OPTICAL  DICTIONARY.  127 

Ophthalmoptoma     (-mop-to'-mah) .     Protrusion     of 
the  eyeballs. 

Ophthalmorrhagia     (-mor-rha'-gee-ah) .       Hemorrh- 
age from  the  eye  or  orbit. 

Ophthalmorrhexis   (-mor-rex'-is) .     The  bursting   of 
the  eyeball. 

Ophthalmoscope  (of-thar-mo-scope).  An  instru- 
ment for  observing  the  interior  of  the  eye,  and 
thus  determining  the  appearance  of  the  media, 
"  the  condition  of  the  retina,  choroid,  and  optic 
nerve,  and  the  state  of  the  refraction. 

The  Ophthalmoscope  consists  of  a  round  mirror, 
with  a  small  perforation  in  the  center.  The 
surface  of  the  mirror  is  usually  concave.  The. 
more  improved  ophthalmoscopes  have  a  rever- 
sible mirror,  one  side  of  which  is  flat  and  the 
other  concave.  In  addition  to  this  there  are 
located  on  the  back  of  the  ophthalmoscope 
several  wheels  which  contain  a  great  variety  of 
convex  and  concave  lenses.  By  rotating  these 
wheels  the  different  lenses  contained  in  them 
can  be  thrown  immediately  behind  the  aperture 
in  the  mirror. 

There  are  two  methods  of  examining  the  eyes 
with  the  ophthalmoscope,  viz.:  the  indirect  and 
the  direct. 

The  indirect  method  is  not  of  much  value  ^o 
far  as  estimating  the  refraction  of  the  eye  is  con- 
cerned, but  gives  a  good  view  of  the  fundus  of 
the  eye,  enabling  us  to  examine  in  minute  detail 
the  optic  disc  and  the  blood-vessels  of  the  retina; 
also  to  observe  whether  any  diseased  condition 
exists  in  the  interior  of  the  eyeball. 


128  LEWIS  POCKET] 

To  perform  this  method  successfully,  we  seat 
our  patient  in  the  dark  room  and  place  a  light, 
either  an  argand  gas-burner,  an  electric  light,  or 
any  ordinary  kerosene  student's  lamp,  at  the 
side  and  slightly  back  of  the  patient's  head.  If 
we  wish  to  examine  the  left  eye  we  place  the 
light  on  the  left  side  of  the  patient's  head,  and  if 
we  wish  to  examine  the  right  eye,  on  the  right 
side.  We  place  the  light  just  far  enough  back 
of  the  head  to  avoid  illuminating  the  patient's 
face.  We  take  our  seat  in  front  of  the  patient 
and  hold  our  ophthalmoscope  at  the  focal  dis- 
tance  of   its   mirror,   reflect   the   light   into   the 


patient's  eye,  and  look  through  the  sight  hole 
in  our  mirror.  The  next  step  is  to  place  a  strong 
convex  lens  immediately  in  front  of  our  patient's 
eye.  With  our  mirror  we  illuminate  the  retina, 
and  the  rays  emanating  from  the  eye  will  leave  it 
as  parallel  rays  in  cases  of  emmet^opia;  as  diver- 
gent rays  in  hypermetropia;  and  as  convergent 
rays  in  myopia.  These  rays  will  be  brought  to 
a  focus  by  the  convex  objective  glass  which  we 
hold  close  to  the  eye  under  examination. 

We  direct  our  patient  to  look  slightly  inward 
while  making  this  examination,  in  order  to  bring 
the  optic  disc  into  view.  It  will  be  remembered 
that  the   optic   disc   is   situated   slightly  to   the 


OPTICAL  DICTIONARY.  129 

inner  or  nasal  side  of  the  center  of  the  retina,  so 
that  when  our  patient  looks  slightly  inward,  the 
back  part  of  the  eye  naturally  moves  outward, 
bringing  the  optic  disc  on  a  line  with  our  vision. 
The  rays  emanating  from  our  patient's  eye  will 
be  brought  to  a  focus  by  the  convex  objective 
glass. 

In  the  hypermetropic  eye  the  image  of  the 
optic  disc  will  look  larger  than  it  does  in  emme- 
tropia,  because  the  rays  from  a  hypermetropic 
eye  are  divergent,  and  will  consequently  be 
brought  to  a  focus  beyond  the  focal  distance  of 
the  convex  objective  glass,  and  on  slightly  with- 
drawing our  objective  glass  we  will  note  that  the 
size  of  the  optic  disc  decreases. 

It  must  always  be  remembered  in  using  this 
method  of  examining  the  eye,  that  we  do  not 
see  the  back  part  of  the  eye  itself,  but  simply  an 
inverted  image  of  the  fundus  of  the  eye  formed 
in  the  air  between  the  objective  lens  and  our 
own  eye. 

In  emmetropia  the  optic  disc  will  look  smaller 
than  it  does  in  hypermetropia,  and  larger  than 
in  myopia.  On  slowly  withdrawing  the  objec- 
tive lens  from  the  emmetropic  eye  the  optic  disc 
will  neither  increase  nor  decrease  in  size,  because 
the  rays  which  emanate  from  an  emmetropic 
eye  will  be  parallel,  and  hence  will  at  all  times 
be  brought  to  a  focus  exactly  at  the  focal  distance 
of  the  convex  objective  glass. 

In  myopia  the  image  of  the  optic  disc  will 
Appear  smaller  than  in  emmetropia  and  much 
smaller  than  in  hypermetropia.  On  gradually 
withdrawing  the  objective  glass  the  optic  disc 
will  increase  in  size. 


130  LEWIS  POCKET 

In  cases  of  astigmatism  the  optic  disc  usually 
looks  oval,  and  on  withdrawing  the  glass  it  will 
increase  or  decrease  more  rapidly  in  one  meridian 
than  in  one  at  right  angles  to  it. 

In  making  the  direct  ophthalmoscopic  exam- 
ination we  also  use  a  concave  mirror,  and  arrange 
the  position  of  the  light  similar  to  that  described 
for  making  the  indirect  examination,  but  in  this 
case  we  place  our  own  eye  very  close  to  that  of 
the  patient.  We  place  our  ophthalmoscope 
at  a  distance  of  about  two  inches  from  the 
patient's  eye,  and  place  our  own  eye  immediately 


behind  the  perforation  in  the  mirror.  It  is 
necessary  in  this  examination  that  neither  the 
patient  nor  the  operator  shall  use  any  accommo- 
dation whatever,  and  in  order  that  this  may  be 
thoroughly  accomplished  it  is  well  to  place  the 
patient  under  the  influence  of  atropine,  assum- 
ing that  the  operator  has  thorough  control  of 
his  own  accommodation  and  can  suspend  it  at 
will. 

Upon  throwing  the  light  into  the  emmetropic 
eye,  we  illuminate  the  retina,  and  a  set  of  rays 
immediately  starts  from  each  point  in  our  pa- 
tient's retina  and  passes  out  of  the  eye.  Each 
ray  of  each  set  is  parallel  to  the  other  rays  in 
the   same    set.     Therefore,    if    the    operator   be 


OPTICAL  DICTIONARY.  131 

emmetropic  himself  he  will  be  able  to  distinctly 
see  the  details  of  the  fundus  in  the  back  part  of 
his  patient's  eye,  because  the  rays  leave  the 
patient's  eye  as  parallel  rays,  and  the  operator's 
eye  being  also  emmetropic  is  adapted  for  parallel 
rays  and  hence  he  has  each  point  on  his  patient's 
retina  represented  by  an  exact  focus  on  his  own 
retina. 

It  can  readily  be  seen  that  if  a  patient  has 
used  any  accommodation  the  rays  would  leave 
his  eye,  not  as  parallel,  but  as  convergent  rays, 
and  therefore  the  operator  would  have  been 
unable  to  distinctly  see  the  details  of  the  fundus. 
On  the  other  hand,  if  the  patient  had  been  under 
the  influence  of  atropine  and  the  rays  had  left 
the  eye  as  parallel  rays  striking  the  observer's 
emmetropic  eye,  as  parallel  rays,  they  would 
not  focus  upon  the  operator's  retina  if  he  had 
used  any  accommodation.  Hence  the  necessity 
of  thorough  relaxation  of  accommodation  in 
both  the  patient  and  operator. 

We  will  next  suppose  that  the  hypermetropic 
eye  is  being  examined  by  an  operator  who  is 
emmetropic.  The  rays  of  light  will  leave  the 
hypermetropic  eye  as  divergent  rays  and  there- 
fore will  not  focus  upon  the  retina  of  the  observ- 
er's emmetropic  eye,  and  hence  he  will  be  unable 
to  distinctly  see  the  details  of  the  fundus  in  his 
patient's  eye.  He  now  rotates  the  wheel  on  the 
back  of  his  ophthalmoscope,  throwing  different 
lenses  into  the  aperture  of  the  mirror,  until  finally 
he  strikes  one  which  enables  him  to  distinctly 
see  his  patient's  retina.  The  glass  which  pro- 
duces this  result  will  represent  the  measure  of 
his  patient's  hypermetropia.     In  order  that  the 


IJ2  LEWIS  POCKET 

operator  may  distinctly  see  the  hypermetropic 
retina,  he  must  use  a  convex  glass  strong  enough 
^    to  render  parallel  the  divergent  rays  which  are 
leaving  his  patient's  eye. 

In  myopia  the  patient's  eye  is  too  long, 
and  the  rays  of  light  which  leave  the  myopic 
eye  will  therefore  leave  as  convergent  rays  and 
focus  in  front  of  the  observer's  retina,  so  that  in 
this  case  he  will  also  be  unable  to  distinctly  see 
the  fundus  of  his  patient's  eye,  and  as  in  the  case 
of  the  hypermetropic  eye  he  rotates  the  wheel 
on  his  ophthalmoscope  until  he  is  able  to  dis- 
tinctly see  the  retina  of  the  myopic  eye.     The 


glass  which  accomplishes  this  result  is  the  meas- 
ure of  the  patient's  myopia. 

In  order  that  he  may  distinctly  see  the  back 
of  this  eye,  a  concave  glass  must  be  used  strong 
enough  to  render  parallel  the  convergent  rays 
which  are  leaving  the  myopic  eye. 

It  is  usually  conceded  that  in  astigmatism 
the  ophthalmoscope  is  of  little  or  no  value.  It 
is  true  that  we  may  be  able  to  see  the  blood-ves- 
sels and  the  edges  of  the  optic  disc  clearer  in  one 
meridian  than  in  another,  and  that  we  may  use 
a  glass  strong  enough  to  render  plain  the  meri- 
dian which  was  at  first  blurred,  and  thereby  dim 
the  meridian  which  was  first  seen  plainly.     The 


OPTICAL  DICTIONARY.  133 

glass  which  clears  up  the  meridian  which  seemed 
blurred  at  first  would  be  the  measure  of  the 
ametropia  in  the  meridian  at  right  angles  to  it. 

It  must  also  be  remembered  that  if  the  opera- 
tor is  not  emmetropic  he  must  either  have  his 
own. refraction  properly  corrected  by  glasses,  or 
he  must  make  deductions  or  additions,  as  the 
case  may  be,  to  or  from  whatever  glass  clears  up 
the  retina  in  the  patient's  eye.  For  instance,  if 
the  operator  knows  himself  to  be  hypermetropic 
to  the  extent  of  one  dioptre,  and  on  examining 
his  patient's  eye  he  finds  that  a  plus  3-D.  glass 
is  required  to  enable  him  to  see  the  details  of  hia 
patient's  fundus,  he  then  knows  that  his  patient 
has  two  dioptres  of  hypermetropia,  because  one 
of  the  three  was  required  to  correct  his  own  eye, 
and  likewise  if  he  had  been  examining  a  myopic 
eye  and  found  that  a  minus  2-D.  lens  was 
required  to  see  his  patient's  retina,  he  would 
know  that  his  patient  had  three  dioptres  of 
myopia,  because  he  himself  was  one  dioptre 
hypermetropic. 

Ophthalmostat  (of-thal'-mo-stat) .    An  eye-speculum. 

Ophthalmula  (of-thal'-mu-lah).     A  cicatrix  located 
upon  the  eye  or  its  appendages. 

Optic.     That  which  pertains  to  the  science  of  light,^ 
and  also  to  the  eye  itself,  together  with  its  func- 
tions. 


V 


Optic  Atrophy.  A  partial  or  total  loss  of  sight 
due  to  atrophy  of  the  optic  nerve. 

Optic  Axis.  A  line  drawn  through  the  center  of  the 
cornea,  through  the  nodal  point  to  the  inner  side 
of  the  macula  lutea. 


V 


134  LEWIS  POCKET 

Optic  Nueritis.     Inflammation  of  the  optic  nerve. 
Optical.     Pertaining  to  the  organ  of  vision. 

Optical  Center.  A  point  on  line  with  the  thickest 
point  of  a  plus  sphere  or  the  thinnest  point  of  a 
minus.  A  ray  of  light  when  passing  through  the 
optical  center  of  a  lens  will  always  emerge  paral- 
lel to  the  incident  ray  or  in  the  same  plane. 

Optical  Corrections.  Lenses  that  change  the  direc- 
tion of  light  rays  entering  the  eyes  to  such  an  ex- 
tent that  the  eyes  are  adapted  to  receive  and 
focus  them  upon  the  retina,  creating  artificial 
emmetropic  conditions  when  ametropic  condi- 
tions exist. 

Optic  Commissure  (kom'-mis-ur).  The  linking  or 
joining  together  of  the  right  and  left  optic  nerve. 

Optic  Disc.  That  spot  on  the  retina  which  marks 
the  entrance  of  the  optic  nerves  into  the  eye.  It 
is  also  called  the  blind  spot,  or  papilla. 

Optic  Excavation.     The  depression  in  the  optic  disc. 

Optic  Nerve.  The  nerve  which  forms  a  communica- 
tion between  the  brain  and  the  organ  of  vision 
It  transmits  retinal  sensations  to  the  centers 
of  perception  in  the  brain,  there  to  be  translated 
into  sight.     (See  cut,  page  135.) 

Optic  Papilla  (pap-il'-lah).  The  elevation  of  the 
optic-nerve  head;  also  called  the  optic  disc  and 
blind  spot. 

Optician  (op-tish'-an).  A  person  skilled  in  the 
manufacture  of  optical  instruments. 


OPTICAL  DICTIONARY. 


135 


Optics.  That  part  of  the  science  of  physics  which 
deals  with  the  transmission  of  Hght,  the  laws  of 
refraction,  reflection,  and  the  phenomena  of 
vision. 

Optic  Tract.  The  optic  nerve  between  the  visual 
centers  and  the  optic  commissure. 


HEAD  OF  THE, OPTIC  NERVE. 

,  Opthalmoscopic  view  of  the  Optic  Disc.  The  small  excava- 
tions seen  around  the  center  is  the  Lamina  Cribrosa.  The 
Papilla  is  encircled  by  the  white  Scleral  Ring  (c),  also  the 
dark  Choroidal  Ring  marked  (d) , 

,  Longitudinal  Section  of  Head  of  Optic  Nerve;  r,  the  Retina; 
b,  Optic  Excavation  and  Canal  for  Central  Artery  (porus 
opticus);  ch,  the  Choroid;  E,  Optic  Nerve;  e,  the  narrow 
interspace  which  corresponds  to  the  Scleral  Ring  seen  by  the 
Ophthalmoscope;  s,  Sclerotic;  ci.  Entrance  of  short  Ciliary 
Artery. 


136  LEWIS  POCKET 

Optist  (op'-tist).     A  person  skilled  in  optometry. 

Optogram  (op'to-gram).  A  faint  image  stamped 
on  the  retina  for  a  brief  period. 

Optometrist.  One  who  measures  the  eye's  refrac- 
tion. 

Optometry  (op-tom'-e-try) .  The  science  and  art  of 
employing  the  various  methods  of  measuring  the 
optical  state  of  the  eye. 

^   O'ra  Serra'ta.     The  anterior  limit  or  edge  of  the 
retina. 

Orbicularis  Palpebrarum.  The  circular  muscle  of 
the  eyelids. 

Orbi cuius  Ciliaris.  A  zone  of  about  one-sixth  of 
an  inch  in  width.  It  is  directly  continuous  with 
the  anterior  part  of  the  choroid. 

Orbit  (or'-bit).  The  bony  socket  in  which  the  eye- 
ball is  placed.  The  orbit  is  made  up  of  seven 
bones:  the  Superior  Maxillary,  Frontal,  Lachry- 
mal, Palate,  Malar,  Ethmoid,  and  Sphenoid. 
The  orbits  are  conical  in  shape  with  their  apices 
extending  backward  and  toward  each  other 
while  the  front  or  base  of  the  cone  is  open,  leav- 
ing the  eyeballs  to  be  protected  by  the  eyelids  in 
front. 

Orbital  (or'-bit-al).     Pertaining  to  the  orbit. 

Origin  (or'-ij-in).  The  more  fixed  end  of  a  muscle; 
for  instance,  the  end  attached  to  the  bone  of  the 
orbit. 


OPTICAL  DICTIONARY.  137 

Orthochromatic  (or-tho-chro-mat'-ic) .  A  term  used 
by  photographers  denoting  that  the  colors  are 
normal  or  correct. 

Orthometer  (or-thom'-e-ter).  An  instrument  for 
finding  the  exact  relative  protrusion  of  the  two 
eyeballs. 

\,  Orthophoria  (-f oh'-ree-ah) .  That  condition  in  which 
the  eyes  are  properly  placed  with  respect  to  each 
other.     Perfect  muscular  balance. 

Orthoptic  (or-thop'-tic) .  Correcting  heterophoria, 
or  strabismus,  by  means  of  the  prism  exercise. 
This  is  accomplished  by  placing  the  base  of  the 
prism  over  the  strong  muscle,  thus  causing  the 
weak  muscle  to  contract  or  draw  the  eye  tojv^ard 
the  apex  of  the  prism  in  order  to  see. 

Orthoscope  (or'-tho-scope).  An  instrument  for 
neutralizing  the  refraction  of  the  cornea  by  ex- 
amining it  through  water. 

Orthoscopic  Lenses.  A  lens  with  two  elements — a 
sphere  and  a  prism — so  arranged  that  the  amount 
of  accommodation  and  convergence  should  exactly 
correspond. 

Orthotropia  (or-tho-tro'-piah).  Perfect  binocular 
fixation. 

O.  S.  (Oculus  Sinister).     Left  eye. 

O.  U.  (Ocular  Unati).     Both  eyes. 

Oxyopia  (ox-y-o'-pi-ah).  That  condition  in  v/hich 
the  sight  is  abnormally  acute. 


138  LEWIS  POCKET 

Jr  achyblepharon  (pach-y-blef-ar'-on) .  That  condi- 
tion in  which  the  eyeUds  have  become  thickened. 

Palpebra  (pal'-pe-brah) .     The  eyelid. 

Palpebral  (pal'-pe-bral) .  That  which  relates  to  the 
eyelid. 

Palpebral  Fissure  (pal'-pe-bral) .  The  space  be- 
tween the  free  margins  of  the  eyelids.  The  outer 
angle  of  fissure  is  called  the  external  can  thus; 
the  inner  angle,  the  internal  canthus.  The  small 
space  between  the  lids  and  globe  at  inner  angle  is 
called  the  lacus  lachrymalis. 

Palpebritis  (pal-pe-bri'-tis) .  An  inflammation  of 
the  eyelids. 

Pannus  (pan'-nus) .  Pannus  consists  of  the  new  for- 
mation of  a  tissue  resembling  granulations  directly 
beneath  the  epithelium  of  the  cornea. 

Panophthalmia  (pan-of-thal'-miah) .  An  inflamma- 
tion of  the  entire  eye  structure. 

Panophthalmitis  (pan-off -thal-mi'-tis) .  General  in- 
flammation of  the  eyeball. 

Pantiscopic.     A  lens  tilted  outward  at  the  top. 

Papilla  (pap-il'-lah) .  A  conic  elevation  observable 
at  the  optic-nerve  head.  P.  Lachrymallis,  the 
mound  at  the  inner  canthus  of  the  eye  pierced 
by  the  lachrymal  puncta. 

Papillitis  (pap-il-li'-tis) .  That  condition  in  which 
there  is  an  inflammation  of  the  optic  disc  or 
papilla. 

Papilloretinitis  (pap-il-lo-ret-in-i'-tis) .  Inflamma- 
tion of  the  optic  disc  and  retina. 


OPTICAL  DICTIONARY.  139 

Parablep8is  (par-ab-lep'-sis) .     False  vision. 

Paracentesis  Cornea  (-sen- tee'-sis). Puncture  of  the 
cornea. 

Parallax  (par'-al-lax) .  An  apparent  displacement 
of  an  object,  due  to  change  in  the  observer's  posi- 
tion. 

Parallel  (par'-al-lel) .  That  which  pursues  the 
same  direction,  but  in  a  separate  path. 

Parallelism  (par'-al-lel-ism) .  State  of  being  par- 
allel. That  condition  in  which  the  visual  axes 
of  both  eyes  lie  in  nearly  parallel  paths. 

Paral'ysis.  That  condition  in  which  there  is  a  loss 
of  power  of  voluntary  motion  or  of  sensation  in 
a  part  from  lesion  of  nerve-substance.  Oculo- 
motor p.,  where  the  motor  oculi  nerve  is  affected. 

Paralysis  of  Accommodation.  That  condition  in 
which  the  function  of  the  branch  of  the  third 
nerve  which  supplies  the  ciliary  muscles  has  been 
interrupted  and  the  eye  cannot,  accommodate, 
the  ciliary  muscles  being  in  a  state  of  rest. 

Paralyt'ic.  Pertaining  to,  or  affected  with,  paralysis; 
a  person  who  is  affected  with  paralysis. 

^Paresis  (par'-es-is) .     A  slight  form  of  paralysis. 

Paropsis  (par-op'-sis) .  That  condition  in  which  the 
vision  is  disordered,  and  may  be  due  to  either  a 
false  impression  being  made  upon  the  retina  or 
a  disordered  condition  of  the  mind. 

Passive.  That  which  is  not  active;  for  instance,  a 
muscle  that  is  in  a  state  of  rest. 


140  LEWIS  POCKET 

Pathetic  (pa-thet'-ik) .  That  which  pertains  to  the 
feelings.  The  pathetic  n^.^iscle  is  the  superior 
oblique  muscle  of  the  eye,  which  receives  its  name 
irom  the  fact  that  tho  patheticus,  or  fourth  pair 

•     of  cranial  nerves,  control  its  movements. 

Pathological    (path-o-log'-i-cal).     (See    Pathology.) 

Pathology  (path-ol'-o-je).  The  science  v/hich  haa 
for  its  object  the  knowledge  of  disease. 

Pediculis  Pubis  (ped-ik'-u-lus  pu'-bis).  Crab-louse. 
In  very  rare  cases  they  will  reach  the  eyelashes 
and  flourish  there.  The  lice  cling  close  to  the 
border  of  the  lid,  and  look  like  dirty  scabs;  the 
eggs  are  darker,  and  may  also  be  mistaken  for 
bits  of  dirt.  The  absence  of  inflammation  and 
the  rather  peculiar  appearance  will  lead,  in 
doubtful  cases,  to  the  use  of  a  magnifying  glass, 
by  which  the  question  will  be  settled  at  once. 

Pathologic.     Pertaining  to  diseased  conditions. 

Penumbra  (pe-num'brah).     A  partial  shadow. 

Perception.  The  acquiring  of  impressions  through 
the  senses.  Centers  of  sight  p.,  those  portions 
of  the  brain  that  are  the  sources  of  the  optic 
nerves. 

Perceptivity  (per-sep-tiv'it-e).  Capacity  to  receive 
impressions. 

Perfection  Bifocal .     (See  Bifocal.) 

Pericorneal  (per-i-cor  -ne-al) .  That  which  is  situ- 
ated iiround  the  cornea. 

Perichoroidal  (-koh-roy'-dul).  That  which  sur- 
rounds the  choroid  membrane. 


OPTICAL  DICTIONARY.  141 

Perimeter  (per-im'-e-tur).  An  instrument  for  meas- 
uring the  field  of  vision. 

Periocular  (per-e-ok'-u-lar) .  That  which  encircles 
the  eye. 

Perioptic.     (See  Periocular.) 

Perioptometry  (per-e-op-tom'-et-re) .  Measurement 
of  the  visual  acuity  of  the  retinal  periphery. 

Periorbita  (per-i-or'-bit-a) .  That  which  relates  to 
the  lining  membrane  of  the  eye  socket. 

Periorbital  (per-i-or'-bit-al) .  Around  or  about  the 
eye  socket. 

Periorbitis  (per-e-or'-bi-tis) .  Inflammation  of  the 
lining  membrane  of  the  bones  of  the  orbit.  Orbital 
periostitis. 

Periosteitis  (per-e-os-te-i'-tis) .  Inflammation  of  the 
periosteum. 

Periosteum  (per-e-os'-te-um).  The  tough,  fibrous 
membrane  investing  a  bone. 

Periphacus  (per-if-a'-cus).  The  crystalline  lens 
capsule. 

Periphery  (per-if'-er-y).  Any  outward  part  or  sur- 
face; for  instance,  the  border  of  the  cornea  or 
crystalline  lens. 

V  Periscopic  (per-is-cop'-ic).     A  lens  having  a  concave 
^   and  convex  surface.     Periscopic  lenses  are  also 
called  miniscus  lenses;    taken  from  a  Greek  word 
meaning  a  crescent.     (See  Lens.) 


142  LEWIS  POCKET 

Peritomy  (per-it'-o-me) .  An  operation  for  the  treat- 
ment of  pannus,  by  removing  a  strip  of  the  con- 
junctiva around  the  cornea. 

Perivascular  (per-i-vas'-ku-lar).  Surrounding  a 
vessel. 

Perivasculi'tis.  Inflammation  of  the  sheath  of  a 
vessel.  This  is  an  increase  or  a  hyperplasia  of 
the  connective  tissue  about  the  vessels,  princi- 
pally, and  usually,  the  arteries. 

Perspicilium  (per-spic-il'-i-um).  An  apparatus  to 
enable  an  individual  to  see  minute  bodies,  or 
which  will  improve  the  eyesight. 

Pescorvi'nus.  That  which  is  commonly  known  as 
crow's  foot;  or  wrinkles  at  the  outer  corner  of 
the  eye. 

^^  Petit's  ('anal.  The  space  between  the  suspensory 
ligaments  in  which  the  edge  of  the  crystalline 
lens  is  inserted. 

Phaco  (fak'-o).  Prefix  meaning  of,  or  pertaining 
to,  a  lens,  especially  the  crystalline  lens. 

Phacitis  ^f as-i'-tis) .  Inflammation  of  the  crystal- 
line lens. 

Phacomalacia  (f ak-o-mal-a'-she-ah) .  A  soft  cata- 
ract. 

Phacometer  (f  a-com'-e-ter) .  An  instrument  for 
measuring  the  curvature  of  lenses,  and  so  deter- 
mining their  refractive  power;  if  they  are  cylin- 
drical, will  locate  their  axes. 

Phacosclerosis  (f  a-ko-sde-ro'-sis) .  Hardening  of  the 
crystalline  lens. 


OPTICAL  DICTIONARY.  143 

Phacoscope  (f a''-ko-scope) .  An  instrument  used  for 
viewing  the  accommodative  changes  of  the 
crystaUine  lens. 

Phakitis  (f a-ki'-tis) .  Inflammation  of  the  lens.  A 
supposition  exists  that  the  crystalline  lens  may 
become  inflamed. 

Phantasma  (f an'-tas-mah) .  A  disease  of  the  eye  in 
which  imaginary  objects  are  seen. 

Phengophobia  (f en-go-f o'-bi-ah) .   (See  Photophobia.) 

* 
Phimosis  (fi-mo'-sis)  Constrictioii.    Abnormal  small- 
ness  (as  of  the  palpebral  fissure). 

Pho'rotone.  An  instrument  for  exercising  the  mus- 
cles of  the  eye. 

Phlyctenula  (flik-ten'-u-lah).  A  small  vesicle  or 
blister. 

Phlysis  (fly'-sis).     A  corneal  ulcer. 

Phoroscope.  An  instrument  in  the  form  of  a  head- 
rest, with  a  clamp  attached  so  that  it  may  be  fas- 
tened to  a  table,  and  is  used  as  a  fixed  trial  frame. 

Phosphenes  (fos'-feenz).  A  luminous  sensation, 
caused  by  pressing  on  the  eyeball. 

Photalgia  (fo-tal'-je-ah).  Pain  in  the  eye  arising 
from  too  much  light. 

Photochromatic  (fo-to-chro-mat'-ic).  That  which 
pertains  to  various  colored  lights. 

Photodysphoria.     (See  Photophobia.) 


144  LEWIS  POCKET 

Photology  (fo-tor-o-gy).     The  science  of  light. 

Photometer  (-tom'-e-tur) .  An  instrument  for  test- 
ing the  hght  sense. 

Photonosus  (f o-ton'-o-sus) .  Any  disease  of  the  eye 
which  arises  from  exposure  to  the  glare  of  light. 

^  Photophobia  (f o-to-f o'-bi-ah) .     Intolerance  of  light. 

Photopsia  (f o-top'-si-ah) .  That  condition  in  which 
one  sees  flashes  of  light.  It  is  caused  either  by 
pressure  on  the  eyeballs  or  by  disease  of  the 
brain,  optic  nerve,  or  retina. 

^  Photoptometer  (fo-top-tom'-e-ter).  A  device  for 
measuring  sensitiveness  to  light  by  showing  the 
smallest  amount  of  light  that  will  allow  an  object 
to  become  visible. 

Phthisis  Bulbi  (tis'-sis).       Shrinkage  of  the  eyeball. 

Physiolog'ical.     (See  Physiology.) 

Physiology  (fiz-e-ol'-o-je).  That  department  of 
natural  science  which  treats  of  the  organs  of  the 
body  and  their  functions. 

Physostigmine  (fi-so-stig'-min) .  The  same  as 
eserin. 

Pigment.  The  coloring  matter  in  the  choroid  coat; 
the  iris,  etc. 

Pinguecula  (ping-gwek'-yu-lah).  A  small,  yellowish 
elevation,  situated  in  the  conjunctiva  near  the 
margin  of  the  cornea.     Found  in  old  age. 


OPTICAL  DICTIONARY.  145 

Pin  Hole  Disc.  An  opaque  disc  with  a  pin  hole  in 
the  center,  found  in  the  trial  case.  It  is  placed 
in  the  trial  frame  quite  close  to  the  eye  under 
examination.  This  perforation  gives  passage  to 
a  small  pencil  of  light  which  passes  through  the 
center  of  the  refracting  media  of  the  eye.  If  the 
patient  can  see  better  through  the  pin-hole  the 
refracting  system  is  at  fault,  and  vision  can  be 
improved  by  glasses.  If,  on  the  contrary,  vision 
is  not  improved,  then  we  suspect  a  defect  in  the 
sensibility  of  the  retina  or  the  transparency  of 
the  media  of  the  eye,  and  lenses  will  not  improve. 

Pink  Eye.      A  catarrhal  conjunctivitis.     The  eye- 
V    ball  is  of  a  pink  or  reddish  color.     It  is  a  con- 
tagious   disease    which    occurs  among  cattle  and 

horses  as  well  as  in  man. 

1 
Pladaro'sis.     That  condition  where  there  is  a  soft 
tumor  on  the  eyelid. 

Plane.  When  applied  to  glass  a  fiat  surface  is 
meant.  A  plano-concave  lens  is  a  lens  having 
one  side  concave  while  the  other  side  is  fiat.  A 
plane  disc,  or  a  piano,  is  an  accessory  found  in  the 
trial  case  which  has  two  surfaces,  both  of  which 
are  plane. 

Plastic  (plas'-tik).     Tending  to  build  up  tissues. 

Plica  Semilunaris  (ply'-kah).  A  fold  of  conjunctiva 
near  inner  canthus  of  the  eye. 

Point.  The  far  point  or  punctum  remotum  is  the 
farthest  point  at  which  the  eye  can  see  clearly- 
and  distinctly  with  the  accommodation  at  rest. 
The  near  point  or  punctum  proximum  is  the 
nearest  point  at  which  the  eye  can  see  clearly 


146  LEWIS  POCKET 

with  all  of  its  accommodation  in  use.  P.  of 
Reversal.  In  Retinoscopy,  the  term  is  used  to 
designate  the  point  between  an  erect  and  an 
inverted  image,  where  the  change  from  one  to 
the  other  occurs.  Where  convergent  rays  change 
to  divergent  rays.  The  myopic  far  point  in 
Retinoscopy  is  where  the  movement  of  the 
reflex  appears  neutralized.  In  other  words,  it 
is  that  point  on  one  side  of  which  the  shadow 
movement  is  different  than  on  the  other.  For 
instance,  at  any  position  nearer  the  eye  than 
the  point  of  reversal  the  shadow  will  move 
against  the  mirror,  and  at  any  position  farther 
from  the  eye  the  shadow  will  move  with  tho. 
mirror.  This  refers  to  the  concave  retinoscope. 
With  the  flat  mirror  the  movement  would  b(i 
directly  opposite.  P.  of  Fixation.  The  point 
for  which  accommodation  of  the  eye  is  adjusted. 

Pole.     The  summit  of  a  spherical  surface. 

Polarimeter.  An  instrument  for  measuring  tho 
rotation  of  polarized  light. 

Polarization.  The  production  of  a  condition  in 
light  by  virtue  of  which  all  its  vibrations  take 
place  in  one  plane,  or  in  circles  and  ellipses. 

Polychromatic  (pol-y-chro-mat'-ic).  Possessing 
many  colors. 

Polycoria  (pol-e-ko'-re-ah) .  The  presence  of  more 
than  one  pupil. 

Polyopia    (pol-e-o'-pe-ah).     Multiple    vision. 
Pop-Eyedr     A  large  protruding  condition  of  the  eyes. 


OPTICAL  DICTIONARY.  Ifl 

Po'rus  Opticus.  The  opening  through  the  lamina 
cribrosa  through  which  the  arteria  centralis 
retina  and  veins  pass. 

Positive.  That  condition  which  is  real  and  abso- 
lute. The  positive  surface  of  a  periscopic  lens  is 
the  convex  surface. 

Posterior.     Behind;   back. 

Postocular  Neuritis.  Inflammation  of  part  of  optic 
nerve  behind  the  eysball. 

Presbyopia  (pres-by-o'-pi-ah).  When  as  the  result  of 
age  the  power  of  accommodation  has  diminished 
to  such  an  extent  that  the  eye  cannot  produce 
three  diopters  comfortably,  the  condition  is 
called  presbyopia.  The  average  age  when  this 
state  of  affairs  is  present  is  45,  and  as  age  advances 
the  accommodation  gradually  diminishes  and  the 
*  presbyopia  correspondingly  increases.  The 
amount  of  presbyopia  is  represented  by  the  differ- 
ence between  the  number  of  diopters  of  comfort- 
able accommodation  present  and  three  diopters, 
which  must  be  made  good  by  plus  spheres.  The 
presbyope  sees  well  at  a  distance,  providing  there  is 
no  error  of  refraction,  but  has  difficulty  in  main- 
taining good  vision  for  near  work,  and  the  eyes 
become  tired  after  reading,  especially  at  night. 
He  has  trouble  in  seeing  small  objects  because  he 
has  to  hold  them  far  away,  and  consequently 
gets  a  smaller  visual  angle.  Before  correcting 
presbyopia  it  is  necessary  to  test  the  patient's 
distant  vision  and  correct  any  error  of  refraction. 
Then  place  the  reading  chart  in  his  hand;  if  he 
cannot  read  with  comfort  at  the  distance  he 
wishes  to  hold  it,  add  plus  spheres  of  even  amount 


I4S  LiJilWitt   rUUiVHiT 

in  front  of  his  correction  until  you  find  the  weak- 
est that  will  allow  comfort  in  reading.  The  dis- 
tance for  which  the  presbyope  requires  glasses 
will  also  vary  much  according  to  his  or  her  occu- 
pation; ordinarily,  it  is  thirteen  inches. 

Prescription  (pre-scrip'-shun) .  The  formula  for  the 
lenses  required  by  a  patient  which  are  desig- 
nated by  technical  characters  placed  on  blanks 
arranged  for  this  purpose. 

Principal  Focus.  The  point  where  parallel  rays 
of  light  meet  after  refraction  by  a  convex  spheri- 
cal lens. 

Principal  Meridians.  The  meridians  of  greatest  and 
least  curvature. 

Prism.  When  applied  to  optics  is  a  wedge-shaped 
V  transparent  body  of  glass  having  two  plane  sides, 
employed  for  the  purpose  of  bending  rays  of  light. 
A  prism  is  not  a  lens,  and  a  ray  of  light  is  always 
bent  towards  the  base.  It  is  used  in  making  tests 
for  muscular  insufficiencies,  and  sometimes  pre- 
scribed for  constant  wear  in  cases  of  heterophoria. 

Prism  Diopter.  A  prism  which  has  the  power  to 
bend  a  ray  of  light  passing  through  it  and  to  a 
distance  of  one  metre  beyond,  exactly  one  centi- 
metre. 

Prismatic  (pris-mat'-ic).  That  which  has  the  shape 
or  effect  of  a  prism.  When  a  lens  is  decentered 
it  will  produce  a  prismatic  effect. 

S^  Prisoptometer  (pris-op-tom'-et-er).  An  instrument 
used  for  testing  the  refraction  of  the  eye  by 
means  of  a  revolving  prism. 


OPTICAL  DICTIONARY.  149 

Probe.  A  long  slender  instrument  for  exploring 
wounds.  Lacrimal  p.  is  a  probe  designed  for  use 
on  the  tear  passages. 

Progressive  Myopia.  Myopia  that  is  gradually  on 
the  increase. 

Prophthalmos  (prof-thal'-mos) .  A  bulging  forward 
or  undue  prominence  of  the  eyeball. 

Proptosis  (prop-to'-sis).  A  falling  down  or  sink- 
ing of  a  part. 

Prothesis  Ocularis  (pro-the'-sis) .  The  insertion  of 
an  artificial  eye. 

Protractor  Scale.  A  device  for  indicating  the 
location  of  the  axis  of  a  cylinder  lens. 

Pseudoglioma  (seu'-do-gly-oh'-mah) .  A  circum- 
scribed collection  of  pus  in  the  vitreous. 

Pseudoblepsis  (seu-do-blep'-sis).  That  condition 
in  which  objects  look  different  from  what  they 
really  are. 

Psorophthalmia  (soh-rof-thal'-mee-ah).  That  in- 
flammatory condition  of  the  eye  which  is  accom- 
panied with  itchy  ulcerations. 

Pterygium  (ter-yg'-i-um) .  A  thickening  or  growth 
,  of  the  conjunctiva,  usually  on  the  nasal  side  of 
the  eye  extending  out  toward  the  cornea.  It 
can  be  removed  by  operation,  and  should  be  as 
soon  as  it  reaches  the  cornea;  otherwise  it  will 
grow  over  it  and  impair  vision. 

Ptilosis  (ti-lo'-sis) .  That  condition  where  there  is 
a  falling  out  or  loss  of  the  eyelashes. 


150  LEWIS  POCKET 

Ptosis   (to'-sis).     A  drooping  of  the  upper  eyelid. 

V      This    condition   is   caused   by   paralysis   of   that 

branch  of  the  third  or  motor  oculi  nerve  which 

supplies   the   levator   palpebra  muscle.     It  may 

also  be  caused  by  the  thickening  of  the  upper  lid. 

Puncta  (punc'-tah).  A  small  prominence  or  point. 
(See  Puncta  Lacrimalia.) 

Puncta  Lacrimalia  (punc'-ta  lak-ri-mal'-i-ah).  Two 
small  openings  near  the  nasal  end  of  the  sur- 
face of  each  eyelid,  through  which  the  tear 
passes  into  the  lachrymal  canal. 

Punctum  (punc'-tum).  A  fixed  point.  (See  Punc- 
tum  Remotum  and  Punctum  Proximum.) 

Punctum  Remotum.     (See  Far  Point.) 

Punctum  Proximum.     (See  Near  Point.) 

Pupil  (pu-pil).  The  central  circular  opening  in  the 
iris.  A  contracted  pupil  indicates  inflammation 
of  the  brain,  a  sensitive  retina,  hypermetropia, 
effect  of  opium  or  other  drugs.  A  dilated  pupil 
indicates  effect  of  belladonna  or  other  drugs, 
myopia,  or  paralysis  of  the  third  nerve. 

Pupillary  (pu'-pil-la-ry).     Pertaining  to  the  pupil. 

Pupillometer  (pu-pil-om'-et-er) .  An  instrument  for 
measuring  the  diameter  of  the  pupil. 

Pupilloscopy.     (See   Retinoscopy.) 

Pupillostatometer  (pu-pil-o-stat-om'-et-er)  An  in- 
strument to  measure  the  distance  between  pupils. 

Pyrometer  (py-rom'-e-ter).  An  instrument  for 
measuring  high  degrees  of  heat. 


OPTICAL  DICTIONARY.  151 

Vi^uiz.  Instruction  by  questions  and  answers.  Q. 
class,  a  body  of  students  forming  a  class  for  the 
purpose  of  being  questioned  by  a  teacher.  (See 
last  few  pages.) 


V 


XVadiad   (ra'de-ad).     Towards  the   radial  side. 

Radial  (ra'de-al).     Of  or  pertaining  to  the  radius. 

Radian.  An  arc  of  a  circle  which  is  equal  to  the 
radius,  or  the  angle  measured  by  such  an  arc. 

Tladiant  (ra'-de-ant) .  Diverging,  as  rays  from  a 
centre. 

Radiation  (ra-di-a'-shun) .  Where  rays  of  light  ap- 
pear to  be  thrown  off  from  a  common  center. 

Radius.     The  half  of  the  diameter  of  a  circle. 

Range  of  Accommodation.  The  distance  of  a  pa- 
tient's vision,  or  the  range  between  the  near 
point    and  the  far  point. 

Range  of  Vision.  The  distance  between  the  near 
and  far  point. 

Ray.     The  smallest  imaginary  line  of  light. 

Red-Blindness.  That  condition  in  which  a  person 
is  unable  to  distinguish  red. 

Reflection  (re-flec'-shun) .  Throwing  back  light. 
Reflection  from  a  plane  surface  gives  an  erect 
image,  and  the  angle  of  reflection  is  always  equal 
to  the  angle  of  incidence.  The  image  is  formed 
at  a  distance  behind  the  reflecting  surface  equal 


152  LEWIS  POCKET 

to  the  distance  of  the  object  in  front  of  it,  and  is 
called  a  virtual  image. 

Reflection  by  a  concave  mirror.  Parallel  rays 
falling  on  a  concave  surface  are  reflected  as  con- 
vergent rays  which  meet  at  a  point  called  the 
principle  focus.  The  distance  of  the  focus  from 
the  mirror  is  called  its  focal  length. 

Reflection  from  a  convex  surface.  Parallel  rays 
falling  on  a  convex  surface  diverge  and  never 
meet.  No  matter  what  the  position  of  the  object 
before  a  convex  mirror,  the  image  is  always  vir- 
tual, erect,  and  smaller  than  the  object. 

Reflector  (re-flec'-tor) .     A  device  for  reflecting  light. 

Refracting  Media.  (See  Media.)  R.  System.  A 
lens,  or  combination  of  lenses,  for  the  creation  of 
optical  images. 

Refraction  (re-f rac'-shun) .  The  bending  of  a  ray 
"^  of  light  in  passing  obliquely  from  one  media  to 
another  of  different  density.  Double  R.,  refrac- 
tion in  which  the  incident  ray  is  divided  into 
two  refracted  rays.  ^  Static  R.,  refraction  of  the 
eye  at  rest.'*  Dynamic  R.,  refraction  of  the  eye, 
plus  that  secured  by  accommodation.  (See 
page   153.) 

Refractionist  (re-f rac'-tion-ist) .  One  who  is  skilled 
in  correcting  errors  of  refraction  of  the  eye. 

Refractive  (re-frac'-tive).     Pertaining  to  refraction. 

Refractometer  (re-f rac-tom'-e-ter) .  An  instrument 
for  measuring  refraction. 

Regular  (reg'-u-lar) .     According  to  rule;  normal. 


OPTICAL  DICTIONARY. 


153 


Relative  Index  of  Refraction  is  that  which  is  found 
when  light  passes  from  atmospheric  air  into 
another  medium. 

Relaxa'tion.     A  lessening  of  tension. 

Remedy.  Anything  acting  as  a  cure  for,  or  the 
relief  from,  unhealthy  conditions. 


Ai  it  emtr^t$ 
REFRACTION  BY  PLANE  SURFACE. 

No.  1  ray  oi  light  is  called  the  incident  before  entering  the 
second  medium.  A  ray  passing  from  a  rarer  to  a  denser 
medium  is  refracted  towards  the  perpendicular,  as  shown  in 
the  above  cut.  The  ray  BA  is  refracted  on  striking  the 
glass  MM,  and  again  refracted  on  emerging.  In  passing  from 
a  denser  to  a  rarer  medium,  the  ray  is  refracted  from  the 
perpendicular.  P  represents  a  ray  falling  perpendicular  to 
the  surface  separating  the  two  media.  It  continues  its 
course  without  undergoing  any  refraction. 

No.  2  represents  the  reflected  ray.  The  angle  formed  by  the 
inciclent  ray  with  the  perpendicular  is  always  equal  to  the 
angle  of  reflection. 

The  dotted  line  marked  BA'  represents  the  course  the  No.  1  ray 
would  have  taken  had  it  not  been  refracted. 

The  side  of  the  incident  ray  marked  B  will  be  found  at  R  Ul 
the  reflected  ray,  and  A  at  F. 


154  LEWIS  POCKET 

Reposition  (re-po-zi'-shun).  The  act  of  putting 
back  in  a  normal  position. 

Retina  (ret'-in-a).  On  the  inner  surface  of  the 
choroid,  and  closely  in  contact  with  it,  we  find  the 
internal  or  third  and  most  important  of  the 
ocular  tunics,  the  retina;  to  which,  indeed,  the 
other  two  are  merely  protective  or  containing 
membranes.  The  retina  is  the  immediate  con- 
tinuation of  the  optic  nerve,  which  extends  from 
the  brain  to  the  eyeball,  perforates  the  sclerotic 


CL—  MMCHIL-A    LX/TIM,  THE-  nO&T 
SenSITIVB  PARTOF-TMEr  RfcTl/iM. 

and  choroid,  and  immediately  spreads  out  into  a 
thin  lamina  over  the  surface  of  the  latter,  and  is 
attached  at  two  points  only — at  the  entrance  of 
the  optic  nerve  and  at  its  most  anterior  border, 
the  ora  serrata.  The  point  of  entrance  of  the 
optic  nerve  which  is  known  as  the  optic  disc  is 
nearly  on  the  horizontal  meridian  of  the  globe, 
and  about  one-tenth  of  an  inch  to  the  nasal  side 
of  the  posterior  pole,  so  that  it  is  the  left  eye 
which  is  represented  in  the  cut  under  anatomy. 
The  functions  of  the  retina  are  to  receive  the 
pictures  which  are  formed  within  the  eye  by 
means  of  the  waves  of  light  reflected  from  objects, 


V 


OPTICAL  DICTIONAll/.  155 

and,  through  the  medium  of  the  optic  nerve,  to 
transmit  the  resulting  visual  impressions  to  the 
brain. 

Just  as  the  sense  of  touch  is  not  diffused  uni- 
formly over  the  surface  of  the  body,  but  is  more 
acute  in  some  parts,  for  instance,  the  finger  tips, 
than  in  others,  so  also  the  retina  is  not  equally 
sensitive  to  the  luminous  impressions  over  its 
whole  surface,  but  in  the  highest  degree  a  little 
to  the  temple  side  of  the  posterior  pole,  in  a  part 
known  as  the  macula  lutea,  or  yellow  spot,  which 
may  be  considered  the  real  center  of  the  retina, 
yet  it  is  to  one  side.  From  this  spot  the  sensi- 
tiveness gradually  diminishes  to  its  most  anterior 
edge.  The  retina  does  not  extend  as  far  forward 
as  the  choroid,  but  terminates  a  little  in  front  of 
the  equator,  at  the  posterior  border  of  the  ciliary 
body,  in  a  saw-like  margin  the  rough  edge  of 
which  is  known  as  the  ora  serrata. 

Structures  of  the  Retina  according  to 
Gray. — From  within  outwards  the  layers  of  the 
retina  are  named  as  follows : 

Membrana  limitans  interna. 

Fibrous  layer,  consisting  of  nerve  fi- 

Vesicular  layer,    consisting    of    nerve 

Inner  molecular,  or  granular  layer. 
Inner  nuclear  layer. 
Outer  molecular,  or  granular  layer. 
Outer  nuclear  layer. 
Membrana  limitans  externa. 
Layer  of  rods  and  cones,  or  Jacob's 
Membrane. 

No.  10.    Pigmentary  layer. 


No. 

1. 

No. 

2. 

bers. 

No. 

3. 

cells. 

No. 

4. 

No. 

5. 

No. 

6. 

Noo 

7. 

No. 

8. 

No. 

9. 

\^ 


156  '  LEWIS  POCKET 

Retinal  Reflex,  A  term  used  in  retinoscopy  to 
designate  the  light  reflected  from  the  retina  and 
creating  the  Hght  in  the  pupil. 

Retinitis  (ret-in-i'-tis) .  Inflammation  of  the  retina. 
It  is  characterized  first  of  all  by  a  diffused  cloudi- 
ness of  the  organ.  The  cloudiness  varies  very 
greatly  in  intensity,  although  in  general  it  is 
greatest  in  the  vicinity  of  the  optic  disc,  because 
here  the  retina  is  thickest.  Consequently,  the 
outlines  of  the  optic  disc  become  indistinct  and 
the  vessels  in  the  retina  hazy.  The  function  of 
the  retina  is  impaired  in  proportion  to  the  in- 
tensity and  extent  of  the  inflammation.  In  the 
lightest  cases  vision  may  be  normal,  so  that  the 
patients  complain  simply  of  the  presence  of  a 
light-colored  cloud  before  their  eyes.  But  for 
the  most  part  vision  is  very  considerably  reduced 
both  because  of  the  changes  in  the  retina  itself 
and  because  of  the  accompanying  opacities  in 
the  vitreous.  The  course  of  retinitis  is  always 
rather  sluggish.  It  is  only  in  the  lightest  cases 
that  the  inflammation  abates  completely  within 
a  few  weeks,  and  then  the^  visual  acuity  may 
once  more  become  perfectly  normal.  But  for  the 
most  part  it  takes  several  months  for  all  the 
inflammatory  symptoms  to  disappear  from  the 
retina,  while  the  sight  remains  permanently 
impaired.  Severe  and,  more  particularly,  recurrent 
inflammations  of  the  retina  lead  to  atrophy  of  it, 
pigmentation  frequently  occurring  at  the  same 
time  (through  migration  of  pigment  from  the 
pigment-epithelium) .  When  atrophy  of  the  retina 
has  once  made  its  appearance,  the  sight  is  always 
destroyed,  either  completely  or  all  except  a  small 
remnant,  and  its  restoration  is  no  longer  possible. 


OPTICAL  DICTIONARY.  157 

Retinoscope  (ret'-in-o-scope).  An  instrument 
with  which  an  objective  examination  of  the  diop- 
tric state  or  condition  of  the  eyes  may  be  meas- 
ured.    (Made  in  plane  and  concave.) 

The  plane  is  used  for  retinoscopy  only,  while 
the  concave  can  be  combined  with  a  strong  plus 
lens,  about  20-D.,  and  used  as  an  ophthalmo- 
scope. There  is  also  a  difference  in  the  move- 
ment of  the  shadow  in  retinoscopy.     In  working 


with  the  plane  mirror  between  53  and  60  inches 
the  movement  is  against  in  myopia  of  .75  or  more, 
while  in  hypermetropia,  emmetropia,  or  less  than 
.75  of  myopia  the  shadow  moves  with  the  mirror. 
With  the  concave  it  is  just  the  reverse;  the 
shadow  in  hypermetropia,  emmetropia,  and  a 
small  amount  of  myopia  will  go  against  the  mirror. 
In  more  than  ,75  of  myopia,  the  movement  will 
be  with  the  mirror. 


;5S  LEWIS  POCKET 

It  makes  no  difference  which  you  use,  the  find- 
ings will  be  the  same,  and  you  deduct  from  plus 
and  add  to  minus  findings  the  same  amounts;  it 
depends  on  the  distance  you  are  sitting  from  the 
patient.  When  sitting  at  a  little  over  40  inches 
you  subtract  one  diopter  from  all  plus  findings, 
and  add  — .75  to  all  minus  findings.  When  work- 
ing between  53  and  60  inches  you  subtract  .75 
from  all  plus  findings  and  add  — .50  to  all  minus 
findings. 

Retinoscopy  (ret-in-os'-co-py) .  Hetinoscopy,  or  the 
Shadow  Test,  is  one  of  the  best  and  most  popular 
methods  of  estimating  the  refraction  of  the  eye. 
We  examine  the  movements  of  the  shadow  when 
the  fundus  is  illuminated  by  light  thrown  into  the 
eye  from  a  mirror. 

Retinoscopy  with  the  concave  mirror.  The 
patient  is  seated  in  a  dark  room,  with  the 
light  placed  a  little  above  the  head  and  far 
enough,  back  so  that  it  will  throw  no  direct  rays 
upon  his  face.  It  is  best  to  use  a  shade  around 
the  light  to  prevent  it  from  illuminating  the  walls 
of  the  room,  having  a  hole  an  inch  in  diameter 
in  the  front  and  about  the  center  of  the  flame. 
We  will  now  begin  with  the  examination.  The 
first  case: 

Hypermetropia. — Taking  my  seat  between  53 
and  60  inches  from  the  patient,  holding  the  mirror 
in  my  right  hand  before  my  right  eye,  I  look 
through  the  small  hole  in  its  center  at  the  pupil 
of  the  patient's  eye,  at  the  same  time  reflecting 
the  light  from  the  lamp  to  the  patient's  face. 
The  light  must  not  be  too  strong,  but  just  strong 
enough  to  illuminate  the  eye  of  the  patient.    When 


OPTICAL  DICTIONARY.  159 

you  are  examining  the  right  eye,  have  the  patient 
look  slightly  over  your  right  shoulder,  and  if  the 
left  eye,  have  him  look  over  your  left  shoulder.  As 
a  result  of  this  arrangement  the  pupil  of  the  eye 
under  observation  is  illuminated,  and  has  a  reddish 
color.  It  is  really  the  illuminated  spot  on  the 
retina  seen  through  the  dioptric  media,  and  is 
called  the  fundus  reflex,  taking  its  color  from  the 
blood-vessels  of  the  retina.  The  dark  non- 
illuminated  areas  surrounding  it  are  what  are 
known  as  the  shadows. 

Now,  if  we  tilt  the  mirror  from  right  to  left, 
we  will  notice  the  shadow  in  the  pupil  move  from 
left  to  right,  and  is  said  to  go  against  the  mirror; 
now  we  place  in  the  trial  frame  on  the  patient's 
face  a  plus  .50  sphere,  and  if  this  does  not  reverse 
the  shadow,  increase  its  strength  until  we  find 
the  weakest  plus  sphere  that  will  just  reverse  its 
movements;  we  will  say  in  this  case  it  was  +  2.50. 
As  we  are  examining  the  horizontal  meridian  we 
write  +2.50  on  the  horizontal  arm  of  the  cross. 
We  now  remove  the  lens  and  rotate  the  mirror, 
working  up  and  down  the  vertical  meridian.  The 
shadow  will  move  against  as  before,  and  if  there 
is  no  astigmatism  will  require  the  same  amount 
of  plus  to  reverse  it,  so  we  write  +2.50  on  the 
vertical  arm  of  the  cross. 

The  examination  of  this  eye  being  finished,  we 
then  make  another  cro  ;s,  being  careful  not  to 
change  the  meridians,  and  subtract  +.75  from 
each  arm,  and  write  the  amount  remaining  on 
the  same  arms,  but  on  the  new  cross;  this  will 
be  +1.75.  From  this  cross  we  write  the  prescrip- 
tic  n,  and  having  the  same  power  in  all  meridians, 
the  prescription  will  be   +1.75  sphere. 


160  '        LEWIS  POCKET 

Myopia. — Taking  your  position  as  in  the  pre- 
vious case,  rotate  your  mirror  as  before,  and  if 
there  is  less  than  .75-D  of  myopia  the  shadow  will 
move  against,  and  would  require  plus  to  reverse 
it  in  each  meridian.  We  will  say  that  in  this 
case  it  required  +  .  50  to  reverse  the  shadow  in 
both  meridians.  As  we  subtract  +.75  from  all 
plus  findings  this  will  leave  us  — .25  in  all  meri- 
dians, which  should  be  the  correction  for  this  case. 

Should  there  be  .75-D  or  more,  the  shadow  will 
move  with  the  concave  mirror,  and  must  be  re- 
versed with  the  weakest  minus  lens  in  each 
meridian.  In  this  case  it  required  — 1.50  to  re- 
verse the  shadow  in  the  horizontal  meridian,  and 
the  same  amount  for  the  vertical.  Then  we 
make  a  cross  as  before  and  add  — .50  to  each  arm. 
This  would  make  it  — 2  in  all,  and  the  prescrip- 
tion would  be  — 2  sphere. 

Astigmatism. — Is  a  difference  of  refraction  of 
the  meridians  of  an  eye,  one  meridian  of  the  eye 
possessing  a  greater  dioptric  value  than  the  one 
at  right  angles  to  it.  It  is  evident  that  in  exam- 
ining such  an  eye  with  the  retinoscope,  the  ob- 
serving eye  cannot  watch  both  meridians  at  the 
same  time.  Whenever  there  is  astigmatism  the 
shadow  will  move  faster  in  one  meridian,  and  the 
reflex  will  have  a  band-like  or  straight  edge.  If 
this  bright  band  is  seen  straight  up  and  down  in 
the  vertical  meridian,  it  will  move  faster  across 
the  horizontal  meridian,  and  if  the  shadow  moves 
against  the  mirror,  we  will  use  a  plus  cylinder, 
placing  the  axis  parallel  with  the  bright  band; 
in  this  case  it  would  be  the  90th  meridian.  Had 
the  shadow  moved  with  the  mirror,  we  would 
have  used  a  minus  cylinder;    but  in  either  case 


OPTICAL  DICTIONARY: 


161 


increase  the  strength  of  the  cyhnder  until  j^ou 
find  the  weakest  that  will  just  reverse  the  move- 
ment of  the  shadow.  Then  leaving  this  cylinder 
in  its  position,  work  through  its  axis  and  reverse 
the  shadow  in  this  meridian  with  another  cylinder, 
placing  the  axis  at  right  angles  to  the  one  already 
in  the  trial  frame,  which  would  be  the  180th 
meridian  in  this  case.  Now,  as  you  have  just 
reversed  the  2d  meridian,  make  a  cross  on  your 
paper,  having  its  meridians  correspond  to  those 
examined  in  the  eye,  and  on  each  arm  write  the 


^1. 


1^*       -f-5^.- 


90* 


1800 


90 


power  it  required  to  just  reverse  the  shadow. 
In  doing  this  take  no  notice  of  the  axis  of  your 
cylinder.  The  cross  you  have  already  made  is 
known  as  the  retinoscopic  findings,  so  you  must 
make  another  cross  as  before  and  subtract  .75 
from  all  plus  findings,  and  to  minus  findings 
add  — .50,  and  the  remainder  write  on  the  arm? 
of  the  new  cross,  being  careful  not  to  change  the 
meridians.  From  this  cross  you  write  ^  )\jr 
prescription.  We  will  say  in  this  case  that  the 
retinoscopic  finding  was  +2  in  the  vertical,  or 
90th  meridian,  and  + 1  in  the  horizontal  merid- 
iaUt     Now,  as  we  have  to  subtract  ,75  from  all 


162 


LEWIS  POCKET 


plus  findings  it  will  leave  us  +1.25  in  the  ver- 
tical meridian  and  +.25  in  the  horizontal 
meridian  of  the  prescription  cross.  From  these 
findings,  we  write  the  prescription  without 
changing  the  optical  value  of  the  cross. 

The  prescription  in  this  case  would  be 
+  1 .  25  sph.  O  — 1.  cyl.  ax.     90. 
or  +    .25  sph.  O  +1.  cyl.  ax.  180. 

The  cylinder  always  represents  the  amount  of 
astigmatism  in  the  eye.  The  following  are  a 
few  cases  as  examples: 


■7t50- 


i8o^ 


90** 

Prescription — 

— 1.       sph. 
or  —   .25 'sph. 


-25- 


fSO'' 


BO'' 

+  .  75  cyl.  ax.     90. 
—  .75  cyl.  ax.  180. 


-^. 


.5.50 


-^50 


Prescription — 

—3.50  sph. 
or  — 2.50  sph. 


^S' 


+  1  cyl.  ax.  135. 
— 1  cyl.  ax.    45. 


/35« 


OPTICAL  DICTIONARY.  163 

Retractor  (re-trac'-tor) .  An  instrument  used  for 
drawing  and  holding  the  parts  away  while  under- 
going an  operation,  or  for  any  other  purpose. 

Retrobulbar  (re-tro-bul'-bar) .  That  which  is  situ- 
ated or  occurring  behind  the  eyeball. 

Reversal  Point.     (See  Point  of  Reversal.) 

Rheum  (rume) .     A  watery  discharge  from  the  eyes. 

Rhodopsin  (ro-dop'-sin).  Visual  purple;  pigment 
of  outer  segment  of  retinal  rods. 

Rhytidosis  (rit-id-o'-sis) .  A  wrinkling,  as  of  the 
cornea. 

Rod.  Relates  to  the  retina.  It  is  one  of  the  cell 
elements  of  which  Jacob's  Membrane  is  com- 
posed. These  minute  bodies  are  cylindrical  in 
form,  hence  the  term,  rod  (rods  and  cones). 

Romberg's  Symptoms.  Difficulty  in  standing  when 
the  eyes  are  shut:    a  sign  of  locomotor  ataxia. 

Rota'tion.  Process  of  turning  around  an  axis. 
R.  of  the  Mirror.  A  term  used  in  retinoscopy 
to  indicate  the  movement  of  the  mirror  to  create 
a  movement  of  the  light  area. 


164  LEWIS  POCKET 

5^ac.     A  bag-like  organ. 

Saemisch's  Ulcer  (sa'-mish-ez) .  Infectious  corneal 
ulcer. 

Sarcoma  (sar-ko'-mah) .  A  tumor  made  up  of  a 
substance  like  the  embryonic  connective  tissue. 
It  is  often  highly  malignant.  Sarcoma  of  the 
ciliary  body  is  generally  pigmented,  and  often 
passes  unobserved  until  it  attains  considerable 
size  as  a  brown  mass,  which  was  at  first  con- 
cealed from  view  by  the  iris.  Occasionally  it 
makes  its  first  appearance  at  the  angle  of  the 
anterior  chamber. 

Schematic  Eye  (ske-mat'-ik) .  A  model  or  diagram 
of  the  eye. 

Schlemm's  Canal.  A  lymph  channel  in  the  first 
tunic,  between  the  cornea  and  the  sclerotic. 
(See  Anatomy.) 

Scintillation  (pcin-til-la'-shun).  A  sensation  of 
sparks  before  the  eye. 

V  Scissors  Movement.  A  peculiar  movement  of  the 
retinal  reflex,  resembling  the  opening  and  shut- 
ting of  a  pair  of  scissors.  It  indicates  a  condition 
of  irregular  astigmatism. 

Sclera  (skle'-ra).  The  external  coat  of  the  eyeball, 
or  sclerotic. 

Scleral.     Pertaining  to  the  sclera. 

Sclerectasia  (skle-rec-ta'-si-ah).  A  bulging  state  of 
the  sclera. 


OPTICAL  DICTIONARY.  166 

Sclerectomy  (skle-rek'-to-my) .  Excision  of  a  por- 
tion of  the  sclera. 

Sclerectasis  (skle-rek'-ta-sis).  A  protrusion  of  the 
sclerotic  coat.     (See  Staphyloma.) 

Scleriritomy  (skle-rir-if-o-my).  Incision  of  the 
sclera  and  iris'in  anterior  staphyloma. 

Scleritis  (skle-ri'-tis) .  Inflammation  of  the  sclerotic 
coat. 

Sclerochoroiditis  (skle-ro-cho-roid-i'-tis) .  Inflam- 
mation of  both  the  choroid  and  the  sclerotic  coats 
of  the  eye. 

Scleroconjunctival  (skle-ro-con-junc-ti'-val).  That 
condition  in  which  the  sclera  and  the  conjunctiva 
are  concerned. 

Sclerocorneal  Sulsus  (furrow).  The  angle  or  de- 
pression formed  by  the  difference  in  the  radius 
of  curvature  of  .the  sclerotic  and  cornea.  This 
angle  makes  the  eyeball  stronger  and  more  firm 
at  this  point,  and  it  is  just  inside  this  angle  that 
the  ciliary  muscles  are  attached. 

Sclerocorneal  (skle-ro-cor'-ne-al).  Relating  to  the 
sclerotic  coat  and  cornea. 

Scleroiritis  (skle-ro-i-ri'-tis) .  An  inflammation 
which  involves  both  the  iris  and  sclera. 

Sclerokeratoiri'tis.  Inflammation  of  the  sclera,  cor- 
nea, and  iris. 

Scleronyxis  (skle-ro-nyx'-is) .  A  perforation  of  the 
sclerotic  coat. 


166  LEWIS  POCKET 

Sclerophthaimia  (skle-rof-thal'-mi-ah) .  That  condi- 
tion in  which  the  sclera  overlaps  the  cornea,  so 
that  only  a  portion  of  the  latter  remains  clear. 

Scle'rosed.  That  condition  in  which  a  part  is 
affected  with  sclerosis;,  a  hardening. 

Sclerotic  (skle-rot'-ic) .  The  posterior  five-sixths  of 
the  first  tunic.  It  is  firm,  hard,  and  opaque; 
known  as  the  white  of  the  eye.  It  serves  to  give 
shape  to  the  globe,  protects  its  more  delicate  in- 
terior, and  at  the  same  time  acts  as  a  dark-box 
or  camera.  It  is  to  this  coat  that  the  muscles  are 
attached.  The  sclerotic  is  thickest  in  the  pos- 
terior part,  where  it  has  a  thickness  of  about  one 
millimetre.  It  gradually  diminishes  in  thickness 
toward  the  anterior  part,  becoming  somewhat 
thicker  near  the  cornea,  because  here  the  tendons 
of  the  recti  muscles  are  attached  and  fused  with  it. 
The  sclerotic  consists  of  fine  cotton-like  fibers 
or  connective  tissues,  which  are  united  into  bun- 
dles which  seem  to  be  woven  in  all  directions 
Between  the  bundles  are  found  lymph-spaces, 
which  are  in  part  lined  with  fat  cells. 

Scleroticectomy  (skle-rot-i-kek'-to-my) .  An  opera- 
tion for  cutting  through  any  part  of  the  sclerotic. 

Scotodinia  (sko-to-din'-iah) .  Dizziness,  with  head- 
ache and  dimness  of  vision. 

Scotoma  (sko-to'-mah) .  That  condition  in  which 
V  there  is  a  blind  or  partially  blind  area  in  the 
visual  field.  Sometimes  the  patient  will  com- 
plain of  seeing  dark,  vanishing  cloudy  spots  be- 
fore the  eyes.  Absolute  s.,  a  part  of  the  visual 
field  in  which  there  is  absolute  blindness. 


OPTICAL  DICTIONARY  167 

Scotometer  (sko-tom'-e-ter, .  An  instrument  for 
measuring  scotoma. 

Seborrhea  (seb-or-e'-ah) .  An  abnormal  secre  cion 
of  the  sebaceous  glands. 

Seg'ment.  A  section  of  a  circle.  A  cylindrical  lens 
is  a  segment  of  a  cylinder  which  refracts  rays  of 
light  in  all  meridians  but  one.  This  meridian  is 
known  as  the  axis.  A  spherical  lens  is  a  segment 
of  a  sphere.  A  segment  of  anything  is  one  of 
the  parts  into  which  it  is  divided. 

Serpiginous  (ser-pij'-in-us).  Resembling  a  ring- 
worm. 

Shadow  Test.     (See  Retinoscopy.) 

Sheath.  A  tubular  case  or  envelope.  Optic  s.,  the 
covering  of  the  optic  nerve  formed  by  the  dura 
mater  on  the  outside,  and  the  pia  mater  on  the 
inside,  of  the  subarachnoid  space. 

Shortsightedness.     (See  Myopia.) 

Sight.  The  sense  by  which  external  objects  are 
located  and  seen,  their  color,  size,  and  form  de- 
scribed, as  compared  with  other  objects,  through 
the  medium  of  the  visual  organ. 

Sign.  That  by  which  anything  is  represented.  The 
sign  of  addition  (  +  )  represents  convex  spherical 
and  convex  cylindrical  lenses.  The  sign  of  sub- 
traction ( — )  is  used  to  represent  concave  spheri- 
cal and  concave  cylindrical  lenses. 

Sine.  (A  bent  surface,  curve).  Length  of  a  per- 
pendicular drawn  from  one  extremity  of  an  arc  to 
the  diameter  drawn  through  the  other  extremity; 
the  perpendicular  itself. 


168 


LEWIS  POCKET 


Sinis'trad.     To  or  toward  the  left. 

Skiascope  (ski'-as-kope) .    Better  known  as  the  retin* 
oscope. 

Skiascopy.     (See  Retin^scopy.) 


E 

c 

B 

D  L   N 

P  T 

E   R 

r  z 

B  D  E 

or  L 

.   C   T   G 

»"'" 

Z.OTHKC 

Snellen  Chart. 


Snellen,  M.  D.,  Prof.  H.  Born  in  Holland.  A  pro- 
fessor of  ophthalmology  occupying  the  chair 
at  the  University  at  Utrecht,  Holland.  A  pupi]. 
of  Dr.  F.  C.  Bonders,  whom  he  succeeded  in 
practice  and  his  professorship.  He  devised  a 
chart  consisting  of  letters  and  symbols  by  which 
the  subjective  means  of  measuring  the  range 
of  vision  could  be  uniformly  and  scientifically 
determined.  It  is  held  by  Snellen  that  in  order 
to  distinguish  one  letter  from  another  the  eye 
must  be  able  to  distinguish  the  spaces  between 


OPTICAL  DICTIONARY.  169 

the  lines  which  correspond  to  a  visual  angle  of 
1'.  This  is  true  for  certain  letters,  as,  for  in- 
stance, to  differentiate  between  O  and  C,  where 
the  eye  must  distinguish  the  white  space 
which  interrupts  the  circle  in  C.  The  same 
is  true  for  E  and  F,  but  the  principle  is  *not 
applicable  to  the  other  letters  of  his  series. 
In  a  lecture  on  refraction  by  Landolt,  we  learn 
of  what  great  advantage  it  is  to  determine  the 
visual  acuteness  and  the  refraction  at  the  same 
time.  We  must  determine  the  refraction  at  such  a 
distance  as  shall  exclude  the  accommodation  as 
much  as  possible.  For  this  a  distance  of  twenty 
feet,  or  six  metres,  is  necessary.  We  therefore 
place  our  test  type  at  20  F,  and  see  what  are 
the  smallest  characters  which  each  eye,  separately, 
can  distinguish.  These  types  are  so  designed 
that  at  the  distance  at  which  they  should  be 
seen  they  each  subtend  an  angle  of  5'  at  the 
eye.  And  when  the  letters  marked  20,  or  6  M, 
are  read  from  20  F,  vision  is  said  to  be  normal, 
and  an  eye  with  normal  vision  can  read  any  of 
the  letters  on  the  chart  at  the  distance  at  which 
they  are  marked. 

Snow-blindness.  Long  exposure  of  the  eyes  to  the 
glare  from  snow  gives  rise  to  an  acute  conjunc- 
tivitis, attended  with  intense  pain,  photophobia,' 
and  occasionally  conjunctival  hemorrhages. 

Socket  (sok'-ket).  A  hollow  part  into  which  a  cor- 
responding part  fits. 

Spasm.  An  involuntary  contraction  of  a  muscle. 
Spasm  of  accommodation  is  a  spasmodic  con- 
traction of  the  ciliary  muscles,  thus  increasing  the 


J70  LEWIS  POCKET 

convexity  of  the  crystalline  lens  and  making  the 
eye  appear  to  have  a  higher  refractive  power 
There  are  two  kinds — tonic  and  clonic.  Tonic  s. 
is  where  the  spasm  persists  for  a  considerable  time, 
and  Clonic  s.  is  where  the  muscles  contract  and 
relax  intermittently. 

Spectacles.  A  pair  of  lenses  mounted  in  frames  with 
temples  attached. 

Spectrum  (spec'-trum) .  The  analysis  of  the  seven 
colors  which  after  passing  through  a  prism  be- 
come separated.  * 

Sphere.  A  lens  with  the  same  power  in  all  meri- 
dians. There  are  three  ways  to  grind  a  plus  or 
minus  sphere  of  the  same  value;  namely,  bi- 
concave, plano-concave,  periscopic-concave,  bi- 
convex, plano-convex,  periscopic-convex.  (See 
Lenses.) 

Spheroid  (sphe'-roid) .  That  which  resembles  a 
sphere  in  shape. 

Spherometer.  An  apparatus  for  measuring  the  cur- 
vature of  a  surface. 

Sphincter  (sphinc'-ter) .  A  ring-like  muscle.  The 
sphincter  muscle  of  the  iris  when  contracted 
closes  down  the  pupil.  When  relaxed,  allows  the 
pupil  to  become  dilated. 

Spintherism  (spin'-ther-ism).  That  condition  in 
which  the  patient  complains  of  seeing  star-like 
flashes  of  light. 


OPTICAL  DICTIONARY.  171 

Squint.  Cross  Eyes.  Strabismus.  A  condition  in 
which  there  is  a  deviation  of  the  visual  axis  of 
one  of  the  eyes  from  the  correct  positon  of  fix- 
ation when  looking  at  a  point.  The  deviation 
may  occur  in  any  direction.  (See  Concomitant 
Strabismus.) 

Staphyloma  (sta-fy-lo'-mah).  A  bulging  of  the  cor- 
nea or  sclera.  Anterior  s.,  a  bulging  forward  of 
the  anterior  portion  of  the  eye.  Posterior  s., 
backward  bulging  of  the  posterior  pole  of  the  eye. 

Stat'ic.  Not  in  motion;  in  a  state  of  rest.  The 
static  refraction  is  the  refraction  of  the  eye 
with  the  muscles  '  of  accommodation  at  rest; 
just  the  reverse  to  dynamic  refraction. 

Steato'sis.  That  condition  in  which  we  have  fatty 
degeneration;    disease  of  the  sebaceous  glands. 

Stenopaic  Slit  (sten-o-pa'-ic  slit).  An  accessory  to 
.  be  found  in  any  complete  trial  case,  and  consists 
of  an  opaque  disc  with  a  slit  about  an  inch 
long  and  one  millimetre  wide.  It  is  used 
by  some  refractionists  for  the  purpose  of  finding 
the  two  principal  meridians  in  cases  of  astigma- 
tism. The  disc  is  placed  in  the  trial  frame  in 
front  of  the  eye  we  are  about  to  examine.  The 
patient  is  requested  to  look  steadily  at  the  dis- 
tant chart.  The  disc  is  then  slowly  rotated  until 
a  complete  circle  of  the  eye  is  made,  after  which 
it  is  always  best  to  allow  the  patient  to  rotate 
it  for  himself,  and  to  stop  when  the  best  vision 
is  obtained.  This  would  be  considered  one  of 
the  principal  meridians.  We  then  try  convex 
spheres  in  front  of  the  slit.  If  this  meridian 
should  show  hypermetropia  we  continue  to  in- 


172  LEWIS  POCKET 

crease  the  plus  until  we  find  the  strongest  that 
will  allow  the  best  vision.  We  then  take  note 
of  the  number  or  meridian  on  the  trial  frame,  and 
make  a  cross  on  a  piece  of  paper  at  the  same  angle 
as  the  slit  was  placed  in  the  frame,  and  write  on 
the  arm  of  each,  the  power  of  the  lens  required 
for  correction.  So  far  we  have  only  tested  one 
meridian.     We  now  rotate  the  slit  90  degrees  and 


correct  this  meridian  as  before,  writing  down  the 
power  of  the  lens  used  on  the  second  arm  of  the 
cross.  Now  from  this  cross  we  write  the  pre- 
scription without  adding  or  subtracting,  as  we 
do  in  cases  of  retinoscopy. 

Stereoscope  (ster'-e-o-scope).  An  instrument  com- 
posed of  two  prisms  arranged  in  such  a  way  that 
two  separate  pictures  of  the  same  kind  may  be 
seen  as  one.  This  instrument  makes  the  picture 
more  natural,  as  the  objects  appear  to  stand  out. 


OPTICAL  DICTIONARY  173 

Stereoscopic  Vision  (ster-e-p-scopMr).  Where  we 
have  equal  vision  with  the  two  eyes  and  the  ob- 
jects appear  to  stand  out  in  soHd  form,  and  are 
not  seen  as  flat  pictures. 

Stilling's   Canal.     A   small    canal   leading  from  the 
\^     optic  disc  through  the  vitreous  humor  to  the  lens 
of  the  eye.     (See  Anatomy.) 

Stillicidium  (stil-li-sid'-i-um).  An  overflowing  of 
the  tears  upon  the  cheek  due  to  a  stricture  of  or 
a  narrowing  of  the  nasal  duct.  (Same,  as  epiphora.) 

Stilus  (sti'-lus).  A  small  instrument  made  of  gold 
or  silver  used  for  dilating  the  lacrimal  duct. 

Stoke's  Lenses.  An  instrument  that  was  used  in 
the  diagnosis  of  astigmatism.' 

Stop-needle.  A  needle  with  a  disc  attached 
to  regulate  the  depth  of  penetration. 

Strabismometer  (strab-is-mom'-e-ter) .  An  instru- 
ment for  measuring  the  degrees  of  strabismus. 

Strabismus  (stra-bis'-mus).  That  condition  in 
y  which  the  eyes  turn  away  from  parallelism.  This 
condition  can  be  seen  by  an  observer.  The  cause 
of  strabismus  may  be  due  to  an  uncorrected  error 
of  refraction,  for  when  a  person  has  an  error 
of  refraction  in  one  eye  that  interferes  with  the 
vision  of  its  fellow,  he  will  ^earn  to  turn  the  eye 
with  the  error  to  one  side.\j  Concomitant  s.  is 
that  form  of  strabismus  in  which  one  eye,  although 
deviated,  always  moves  with  the  other,  so  that 
the  amount  of  deflection  remains  the  same. 
Paralytic  s.  is  due  to  paralysis  of  one  or  more  of 
the  extrinsic  muscles,  and  the  eye  remains  sta- 


\ 


174 


LEWIS  POCKET 


tionary.  Hypermetropia  is  responsible  for  80  per 
cent  of  converging  strabismus  on  account  of  the 
ciliary  muscles  and  the  internal  rectus  muscles 
being    supplied    by  one    and    the    same   nerve. 


One  Eye  turning  in. 


Both  Eyes  turning  in. 


Both  Eyes  turning  out. 

When  the  eye  attempts  to  accommodate  in  order  to 
overcome  the  hypermetropia,  the  internal  rectus 
will  contract,  and  if  the  patient  has  not  the  nerve 
energy  to  control  the  external  rectus,  the  eye  will 
turn  in. 


OPTICAL  DICTIONARY.  175 

Strabotomy  (stra-bot'-o-my).  An  operation  calling 
for  the  cutting  of  an  ocular  tendon  for  relief  in 
cases  of  strabismus. 

Strain.     Injury  from  over-use. 

Stye.  Inflammation  of  a  sebaceous  gland  of  the 
eyelid.  It  lies  near  the  border  of  the  lid,  and 
corresponds  to  the  inflamed  gland.  In  a  day  or 
two  the  swelling  at  this  spot  increases,  and  the 
skin  over  it  grows  red,  afterward  shows  a  yellow- 
ish discoloration,  and  finally  is  perforated  near 
the  border  of  the  lids,  with  a  discharge  of  pus. 
After  the  evacuation  of  the  pus  the  inflammatory 
.  symptoms  rapidly  abate,  the  small  abscess- 
cavity  soon  closes,  and  the  entire  process  comes 
to  an  end.     Eye-strain  is  a  common  cause. 

Subarach'noid  Space.  That  space  between  the 
dura  »mater  and  the  pia  mater  which  forms  the 
optic  sheath  and  the  Capsule  of  Tenon. 

Subconjunctival  (sub-con-junc-ti'-val).  That  which 
is  situated  just  beneath  the  conjunctiva. 

Subjective  (sub-jec'-tive).  That  which  pertains  to, 
or  is  perceived  by,  an  individual.  '  Not  percept- 
ible to  any  other  person.  It  refers  to  the  patient 
as  he  sees  objects  or  feels  concerning  his  own  im- 
pressions. 

Subla'tio  Ret'inae.     Detachment  of  the  retina. 

Subluxa'tion.  Where  the  lens  of  the  eye  is  a  little 
displaced,  subluxation  may  consist  in  the  lens 
being  turned  a  little  obliquely,  so  that  one  end 
of  it  looks  somewhat  forward.  This  condition 
may  be  recognized  from  the  unequal  depth  of  the 


176  LEWIS  POCKET 

anterior  chamber.  In  cases  of  luxation,  that  is, 
where  the  lens  has  left  its  place  in  its  capsule,  so 
that  it  partly  covers  the  pupil,  that  part  of  the 
pupil  which  is  a  deep  black  has  no  lens,  while  the 
part  which  contains  the  lens  would  be  of  a  delicate 
gray.  Any  dislocation  of  the  lens  entails  a  con- 
siderable disturbance  of  vision.  If  the  lens  still  I 
lies  behind  the  pupil  the  eye  becomes  very  myopic, 
because  the  lens  is  allowed  to  assume  its  maxi- 
mum convexity  on  account  of  separating  frOm 
the' suspensory  ligaments  which  keep  it  elongatedft 
when  the  eye  is  at  rest.  Invariably  any  tear  in' 
the  suspensory  ligament  results  in  soft  cataract. 
Added  to  this  is  a  considerable  degree  of  astig- 
matism. Dislocations  of  the  lens  usually  entail  I 
secondary  consequences  which  may  be  ex- 
tremely disastrous  to  the  eye,  but  in  those 
cases  in  which  the  dislocation  entails  no  further 
injurious  consequences  than  the  disturbance  of 
vision,  the  treatment  consists  in  prescribing 
suitable  glasses. 

Suborbital  (sub-or'-bit-al) .     Beneath  the  orbit. 

Subretinal    (sub-ret'-in-al).     Situated    beneath    the 
retina. 

Subvolution    (sub-vo-lu'-shun) .     An    operation    for 
the  removal  of  a  pterygium. 

Suction  (suc'-shun).     A  method  by  which  fluid  is 
withdrawn. 

Suffusion  (suf-fu'-zhun).  State  of  being  blood-shot, 
or  of  being  moistened.  A  suffusion  of  tears  is  an' 
excess  of  the  flow  of  tears, 

Super  Cilia.     (Upper  hairs.)     The  eyebrows. 


OPTICAL  DICTIONARY.  177 

Superciliary  (sii-per-cil'-i-a-ry) .  That  which  per< 
tains  to  the  eyebrow. 

Supra  Choroidal  Space.  The  space  between  the 
sclerotic  and  choroid. 

Supraduction,  Sursumvergence.  The  power  of  the 
superior  rectus  muscles. 

Supraorbital   (su-pra-or'-bi-tal) .     Located  over  the 

orbits. 

Sursumduction  (sur-sum-duk'-shun).  The  act  of 
turning  one  eye  up  and  the  other  down.  The 
test  is  made  by  placing  the  base  of  prisms  up  or 
down  until  we  find  the  strongest  with  which  the 
eye  can  see  an  object  singly. 

Sursumvergens  (sur-sum-vur'-jenz).  A  tending  up- 
ward, as  in  vertical  squint. 

Suspensory  (sus-pen'-so-ry).  Serving  to  hold  up  a 
part. 

Suspensory  Ligaments.  The  hyaloid  membrane 
forms  the  hyaloid  sac  in  which  the  vitreous  humor 
is  contained.  It  runs  forward  up  over  the  cDiary 
body,  divides  and  forms  the  suspensory  ligaments, 
which  are  attached  to  the  lens  capsule.  C.  B. 
Lock  wood,  in  a  journal  of  Anatomy  and  Physi- 
ology, vol.  XX.,  part  I. — Ed.  of  15th  English 
edition,  has  also  described  a  thickening  of  the 
lower  part  of  the  Capsule  of  Tenon,  which  he  has 
named  the  suspensory  ligament  of  the  eye.  It 
is  slung  like  a  hammock  below  the  eyeball,  being 
expanded  in  the  centre  and  narrow  at  its  ex- 
tremities, which  are  attached  to  the  malar  and 
lachrymal  bones  respectively. 


V 


178  LEWIS  POCKET 

Symblepharon  (sym-blef '-ar-on) .  Adhesion  of  the 
lids  to  the  eyeball.  This  develops  whenever  two 
opposed  spots  of  the  conjunctiva  of  the  lid  and 
of  the  eyeball  have  raw  surfaces  which  come  into 
contact  with  each  other,  and  in  consequence  be- 
come adherent.  Causes  which  can  give  rise  to 
the  formation  of  raw  surfaces  upon  the  conjunc- 
tiva are  burns  by  the  action  of  heat,  burns  from 
caustic  substances,  diphtheria,  operations,  ulcers 
of  all  kinds,  etc. 

Sympathetic  Ophthalmitis  (sym-pa-thet'-ik  of-thal- 
mi'-tis).  An  inflammatory  condition  of  the  iris 
and  ciliary  body,  which  is  developed  through  an 
injury  or  disease  of  the  opposite  eye. 

Symptoms.  A  perceptible  change  which  indicates 
disease,  or  that  which  indicates  the  existence  of 
something  else.  (See  Objective  and  Subjective 
Symptoms.) 

Synchysis  (syn'-chy-sis) .  Liquefaction  of  the  vitre- 
ous. When  observing  opacities  of  the  vitreous 
with  the  ophthalmoscope,  we  see  that  most  of 
them  float  about  freely  in  the  vitreous.  From 
this  we  would  assume  that  the  framework  of  the 
vitreous  must  have  been  destroyed,  so  that  this 
body  itself  is  converted  into  a  perfectly  liquid 
mass. 

Syndesmi'tis.  That  condition  in  which  there  is  in- 
flammation of  a  ligament  or  of  the  conjunctiva. 

Synechia  (syn-e'-chi-'^h),.  Adhesion,  as  of  the  iris  to 
the  lens  or  cornea.  yPMerior  s.,  adhesions  of  the 
iris  to  the  lens  capsule. \  Anterior  s.,  adhesions  of 
the  iris  to  the  cornea. 


OPTICAL  DICTIONARY.  179 

Synizesis  (sin-iz-e'-sis).     Contraction  of  the  pupil  of 
the  eye. 

Synophthalmus     (syn-of-thal'-mus) .      A     one-eyed 
monster. 

Syntropic  (sin-trop'-ik) .     Turned  in  the  same  direc- 
tion. 

System.     The  bodily  organism.     An  assemblage  of 
parts  or  organs  which  unite  in  a  common  function. 


T»     -A.n  abbreviation  for  tension  or  temperature. 

Tapetum  (ta-pe'-tum) ,  The  luminosity  seen  in  the 
eyes  of  many  beasts.  A  lustrous,  greenish  mem- 
brane seen  in  the  eyes  of  cats. 

Tarsal  Cartilages  (tar'-sal  kar'-til-aj-es).  The  cartil- 
ages that  give  the  eyelid  its  shape. 

Tarsitis  (tars-i'-tis) .  An  inflammation  involving  the 
tarsal  cartilages. 

Tarsoplasty  (tar'-so-plas-ty) .  Plastic  surgery  of  the 
tarsus. 

Tarsorrhaphy  (tar-sor'-a-f e) .  An  operation  upon 
the  eyelids. 

Tarsotomy  (tar-sot'-o-my).  A  surgical  operation 
which  involves  the  cutting  of  the  tarsal  cartilages. 

Tarsus  (tar'-sus).  That  which  forms  the  skeleton 
of  the  eyelid,  giving  it  rigidity  of  form  and  afford- 
ing it  firm  support.  The  tarsus  of  the  upper  lid 
is  broader  than  that  of  the  lower. 


180  LEWIS  POCKET 

Tears.     The  watery  secretion  of  the  lacrimal  glands. 

Teichopsia  (tei-kop'-si-ah).  A  luminous  appearance 
before   the  eyes,  with  a  zigzag,  wall-like  outline. 

Telangiectasis  (tel-an-je-ek'-ta-sis).  Dilatation  of 
capillaries. 

Tendency  (tend'-en-cy).  A  disposition  on  the  part 
of  a  muscle  to  incline  toward  certain  directions. 

Tendon  (ten'-don).  The  fibrous  cords  by  which  the 
muscles  are  attached. 

Tenonitis  (ten-on-i'-tis).  Inflammation  of  the  Cap 
sule  of  Tenon. 

\  Tenon's  Capsule.  The  capsular  non-bony  socket  of 
V  the  eye.  This  extends  forward  as  far  as  the  con- 
junctiva of  the  eyeball  and  backward  nearly  to 
the  optic  nerve.  It  is  thus  open  in  front  and  be- 
hind, and  may  be  said  to  represent  a  broad  ring 
placed  about  the  eyeball.  It  forms  the  articular 
socket  for  the  eyeball,  which  can  move  in  it 
freely  in  all  directions.     (See  Anatoitiy.) 

Tenotomy  (ten-ot'-om-e) .  An  operation  for  cutting 
or  dividing  the  tendon  of  a  muscle. 

Tension  (ten'-shun).  The  condition  of  being 
stretched  or  tense. 

Tensor-tarsi  Muscle  (ten-sor-tar'-si) .  A  very  small 
muscle  located  at  the  inner  canthus  of  the  eye. 
It  takes  its  origin  at  the  crest  of  the  lacrimal  bone, 
and  is  inserted  into  the  tarsal  cartilage  of  the  eye- 
lids. It  is  supplied  by  the  facial  nerve.  Its  use 
is  to  compress  the  puncta  and  lacrimal  sac. 


OPTICAL  DICTIONARY.  181 

Test.  An  examination  or  trial.  T.  type§,  letters  of 
various  shapes  and  sizes  used  in  testing  visual 
power. 

Tetranopsia  (tet-ran-op'-si-a) .  Obliteration  of  one- 
fourth  of  the  visual  field. 

Thermometer  (ther-mom'-e-ter) .  An  instrument 
for  ascertaining  temperatures. 

Thrombosis  (throm-bo'-sis) .  The  formation  of  a 
blood-clot  in  a  vessel  at  the  point  of  obstructioi  . 

Thyroid  (thi'-roid).  Shield-shaped.  T.  Gland  is 
a  vascular  body  situated  at  the  front  and  side  s 
of  the  neck,  and  extending  upwards  upon  er  ( h 

'  side  of  the  larynx.  It  is  a  single  gland,  varying 
greatly  in  size  in  different  individuals. 

Tinea  Tarsi.  Blepharitis  marginalis.  (See  Bleph- 
aritis.) 

Tobacco  Amaurosis.  A  dimness  of  vision  caused 
by  the  excessive  use  of  tobacco,  which  acts  directly 
upon  the  nervous  system.  The  reduction  in  the 
visual  acuity  is  alraost  always  the  same  in  both 
eyes.  Treatment  consists,  first  of  all,  in  absti- 
nence from  tobacco,  and  it  is  probable  that  in 
light  cases  this  alone  is  suiiicient  to  effect  a  cure. 

^   Tonic  Spasm.     A  continuous  involuntary  contrac- 
y    tion  of  the  ciliary  muscles.    This  condition  may 
exist  in  any  muscle. 


\ 


Tonometer    (to-nom'-e-ter) .      An     instrument    for 
measuring  the  tension  of  the  eyeball. 

Toric  IJens.    A  lens  with  a  sphere  and  a  cylinder  on 
the  same  side)  periscopic  in  shape.  (See page 225) 


V 


182  LEWIS  POCKET 

Torsion  (tor'-shun).     A  twisting. 

Toxic  Amblyopia.  Amblyopia  caused  by  a  poison, 
a  common  cause  being  excessive  use  of  tobacco 
or  liquor  or  both. 

Trachoma  (tra-ko'-mah) .  Granular  conjunctivitis. 
Characterized  by  slowly  progressive  changes  in 
the  conjunctiva  of  the  eyelids,  in  consequence  of 
which  this  membrane  becomes  thickened,  vascu- 
lar, and  roughened  by  firm  round  elevations,  in- 
stead of  being  pale,  thin,  and  smooth.  Granular 
disease  is  very  important,  because  it  greatly  in- 
creases the  susceptibility  of  the  conjunctiva  to 
take  on  acute  inflammation  and  to  produce  con- 
tagious discharge.  It  often  gives  rise  to  deformi- 
ties of  the  lid  and  to  serious  damage  of  the  cornea. 
The  conditions  which  favor  the  development  and 
spread  of  trachoma  are  unclean  and  overcrowded 
surroundings  in  which  ventilation  is  neglected, 
and  the  locality  is  damp.  The  disease  is  common 
among  school  children  who  are  poorly  nourished. 

Tract.     (See  Optic  Tract.) 

Transection  (tran-sek'-shun) .  A  section  made  across 
a  long  axis. 

Transillumination  (trans-il-lu-min-a'-shun).  The  in- 
spection of  the  interior  of  an  organ  by  means  of  a 
strong  light. 

Transit.  A  passing  across.  A  term  used  in  re- 
tinoscopy  to  indicate  movement  of  the  light 
area. 

Transi'tional  Zone.  The  posterior  part  of  the  lens 
sac  during  the  stage  of  growth. 


OPTICAL  DICTIONARY.  183 

Translu'cent.  The  quality  of  transmitting  rays  of 
light  without  the  object  being  distinctly  seen. 
(Frosted  Glass,) 

Transparent.  Having  the  property  of  being  clearly 
seen  through. 

Transposition  (trans-po-si'-shun).  Changing  the 
form  of  an  optical  prescription  without  changing 
its  optical  value.  In  order  that  you  may  be  en- 
abled to  give  your  patients  glasses  which  give 
them  the  best  possible  vision,  it  is  necessary  for 
you  to  know  how  to  build  lenses  which  produce  a 
periscopic  effect;  this  periscopic  effect  being  the 
prime  and  important  feature  in  every  instance 
The  term  periscopic  is  applied  to  spectacles  having 
concavo-convex  lenses,  which  enable  the  eye  to 
view  with  equal  likeness  on  all  sides.  When 
lenses  are  not  of  this  description  the  desired  re- 
sult may  be  obtained  by  the  following  rules: 

When  the  sign  of  the  sphere  and  cylinder  are 
alike  (i.  e.,  both  plus  or  both  minus)  add  them  to- 
gether for  the  new  sphere,  prefixing  the  same  sign. 

When  the  sign  of  the  sphere  and  cylinder  are 
different  (i.   e.,   one  plus  and  the  other  minus) 
subtract  for  the  new  sphere,  prefixing  the  sign  ol . 
the  larger  number. 

Always  change  the  sign  of  the  cylinder  to  the 
opposite,  but  do  not  change  its  value. 

Always  change  the  axis  to  right  angl ;  (i.  e., 
move  it  90  degrees). 

For  transposition  of  simple  cylinders,  use  the 
following  rule:  Use  the  numerical  value  of  your 
cylinder  for  the  new  sphere,  prefixing  the  same 
sign,  and  for  the  new  cylinder  use  the  same  value 


184  LEWIS  POCKET 

as  the  original,  but  prefix  the  opposite  sign  and 
change  the  axis  to  right  angle. 

To  convert  cross  cylinders  into  sphero-cylinders. 
apply  the  following  rule:  Use  the  smaller  number 
for  your  sphere  (if  the  numbers  are  alike,  take 
either  one,  keeping  its  own  sign),  and  when  the 
signs  of  the  cylinders  are  alike  (i.  e.,  both  plus  or 
both  minus)  subtract  them  for  your  cylinder, 
prefixing  the  same  sign.  When  the  signs  are 
unlike  (i.  e.,  one  plus  and  the  other  minus)  add 
them  for  your  cylinder,  prefixing  the  sign  of  the 
remaining  cylinder.     And  also  its  axis. 

If,  after  transposing  cross  cylinders,  your  pre- 
scription is  not  periscopic,  make  it  so  by  trans- 
posing again  by  one  of  above  rules. 

Below  find  a  few  examples  in  transposition,  with 
their  answers:    (See  page  215.) 

Example,    +  3  sph.  O  — 2  cyl.  ax.     60. 
Answer,      -f- 1  sph.  O  +2  cyl.  ax.  150. 
Example,    +2  sph.  o   +2  cyl.  ax.     90. 
Answer,      +4  sph.  o  — 2  cyl.  ax.  180. 
Example,    +4  cyl.  ax.  45  o   +2  C3^^  ax.  135. 
Answer,      +  2  sph.  Q  +  2  cyl.  ax.     4o. 
Example^  — 3  cyl.  ax.  20  o  +3  cyl.  ax.  110. 
Answer,      — 3  sph.  o  +6  cyl.  ax.  110. 
Example,    + 1  cyl.  ax.  60. 
Answer,      + 1  sph.  o  — 1  cyl.  ax.  150. 

Traumatic  (trau-mat'-ik) ,  Of,  caused  by,  or  per- 
taining to,  an  injury. 

Trembling  Eyes.     (See  Nystagmus). 

Trial  Case  (and  how  to  use  it).  The  ordinary  trial 
case  contains  about  thirty  pairs  of  convex  and 
the   same   number   of   concave   spherical   lenses, 


OPTICAL  DICTIONARY.  185 

ranging  from  0.1 2-D.  up  to  20-Diopters;  twenty- 
pairs  of  convex  and  the  same  number  of  con- 
cave cylindrical  lenses  ranging  from  0.1 2-D,  up 
to  6-D.;  at  least  ten  prisms  from  1  to  10 
degrees;  a  plain  red  tinted  glass;  some  shades 
of  smoked  glasses;  an  opaque  disc;  stenopaic 
slit;  pinhole  disc;  a  ground  glass  disc;  a  Maddox 
rod,  or  double  prism,  and  a  retinoscope;  two  trial 
frames,   one    having    three    cells   to   be   used   in 


Trial  Case. 

fitting,  the  other  two  cells,  so  that  we  may  allow 
a  patient  to  wear  his  correction  for  a  short  time 
and  still  have  one  to  use.  The  patient  is  seated 
20  feet  from  the  test  card,  which  must  be  well 
illuminated,  and  shades  arranged  so  that  the  light 
will  throw  no  direct  rays  on  the  patient's  face. 
Place  a  small  table  holding  your  trial  case  on  the 
patient's  right-hand  side;  seat  yourself  at  the 
table  with  your  back  to  the  reading  chart.  Now 
you  will  find  yourself  in  a  very  easy  position  to 
change  the  lenses.     The  trial  frame  is  placed  upon 


186  LEWIS  POCKET 

the  patient's  face  and  adjusted,  so  that  he  will 
look  through  the  center  of  the  lenses,  having  the 
frame  as  near  the  face  as  possible.  Now  you  are 
in  a  position  to  begin  testing.  First  place  the 
opaque  disc  over  the  left  eye,  always  making  it  a 
rule  to  test  the  right  eye  first,  as  you  will  find  all 
prescription  blanks  made  out  in  this  way.  Now 
instruct  your  patient  to  read  the  smallest  line  of 
letters  that  he  can  see  with  the  naked  eye.  We 
will  say  in  this  case  he  read  the  line  marked  60. 
As  he  is  seated  20  feet  from  the  chart,  vision  with 
the  naked  eye  is  20/60.  You  must  always 
remember  what  the  vision  with  the  naked  eye  is, 
so  that  you  will  be  able  to  judge  whether  or 
not  the  vision  is  improved  with  the  correction. 
Now  you  take  a  plus  sphere  from  the  trial  case, 
say  plus  .50-D.,  place  it  before  the  right  eye,  ask- 
ing the  patient  to  again  read  the  smallest  type 
that  he  can  see  clearly.  Should  the  patient 
not  read  as  well,  the  case  may  be  one  of  emme- 
tropia,  myopia,  or  astigmatism;  but,  on  the  other 
hand,  if  he  reads  just  the  same  as  before,  or  a 
line  better,  it  is  a  case  of  hypermetropia,  and  we 
will  now  proceed  to  work  out  a  case  of  each  kind. 
Hypermetropia. — Place  the  trial  frame  on  the 
patient's  face,  cover  the  left  eye  with  the  opaque 
>  disc,  and  ask  the  patient  which  is  the  smallest 
line  he  can  read  correctly.  In  this  case  we  will 
say  he  read  line  numbered  50.  Then  his  vision 
will  be  20/50.  Now  we  place  before  this  right 
eye  a  plus  .50  sphere,  and  if  the  patient  reads  the 
same  or  a  line  better,  it  is  surely  a  case  of  hyper- 
metropia. Now,  as  a  plus  will  always  relax  ac- 
commodation, and  we  do  not  want  any  eye  to 
accommodate  for  20  feet,  or  farther,  we  will  add 


OPTICAL  DICTIONARY  187 

more  plus  in  the  following  manner:  take  a  plus 
1  sphere  and  place  it  in  the  second  cell  of  your 
trial  frame,  then  withdraw  the  plus  .50.  In  this 
way  the  eye  will  not  be  left  uncovered;  again  ask 
the  patient  to  read,  and  should  he  read  as  well 
as  before  we  will  increase  the  plus  sphere  until 
the  smallest  line  that  he  reads  the  best  becomes 
blurred,  then  we  will  know  that  he  has  relaxed 
all  the  accommodation  he  had  in  use;  that  being 
the  object  of  the  fogging  system.  Then  draw  the 
patient's  attention  to  astigmatic  wheel,  asking 
him,'' are  all  the  spokes  in  the  wheel  equally  clear 
and  of  the  same  density?"  If  there  is  no  astig- 
matism the  patient  will  see  the  wheel  uniformly. 
In  that  case  we  would  ask  him  to  again  look  at 
the  reading  chart,  and  gradually  reduce  the 
strength  of  the  plus  sphere,  until  we  find  the 
strongest  that  will  allow  the  best  vision.  This 
will  be  his  correction.  On  the  other  hand,  had 
the  patient  told  you  that  the  wheel  did  not  look 
uniform,  but  that  one  or  more  of  the  spokes  were 
much  darker,  it  would  indicate  astigmatism,  and 
we  would  ask  the  patient  which  spoke  appeared 
the  most  clearly.  Now,  suppose  he  says  "it  is 
the  vertical,"  or  th?>  spoke  running  from  12  to  6, 
then  as  we  wish  to  know  if  the  patient  sees  the 
spoke  quite  clearly,  we  will  ask  him  to  count  the 
lines  in  the  spoke.  Should  he  count  the  right 
number  we  will  consider  he  is  seeing  it  clearly, 
and  to  make  sure  that  he  is  not  still  accommo- 
dating before  we  correct  the  astigmatism,  we  will 
increase  the  plus  sphere  (already  in  the  trial 
frame)  until  we  just  about  blur  all  the  spokes  in 
the  wheel;  then  reduce  your  sphere  a  quarter  D. 
at  a  time,  at  the  same  time  asking  the  patient  to 


188  LEWIS  POCKET 

inform  you  when  one  of  the  spokes  comes  out 
clearly,  and  he  can  count  the  lines.  Whatever 
plus  sphere  you  have  in  the  frame  at  this  time, 
place  in  the  cell  nearest  the  eye;  or,  a  better  way 
would  be  to  place  a  plus  sphere  of  the  same 
strength  as  the  one  , already  in  the  frame  in  the 
cell  nearest  the  eye  before  removing  the  one  in 
front.  In  this  way  you  will  move  the  lens  in  the 
frame  without  exposing  the  naked  eye.  It 
will  then  be  out  of  the  way  while  using  the  cylin- 
der. Now  take  from  your  trial  case  the  weakest 
minus  cylinder  and  place  it  in  the  trial  frame 
with  the  axis  at  right  angles  to  the  plainest 
spoke  seen.  Should  this  fail  to  make  the  wheel 
look  uniform,  increase  the  strength  of  your 
cylinder  until  you  find  the  weakest  that  will 
make  the  wheel  look  equal  in  density  in  all  its 
spokes.  When  you  have  done  this,  draw  the 
patient's  attention  to  the  reading  ci:iart,  and 
gradually  reduce  the  strength  of  your  plus 
sphere  while  it  improves  the  distant  visioft.  In 
other  words,  the  strongest  plus  sphere  combined 
with  the  weakest  minus  cylinder  that  corrected 
the  astigmatism  is  the  patient's  correction  for 
constant  use. 

Myopia. — Seat  the  patient  as  in  the  previous 

'  case.  Cover  the  left  eye  with  the  opaque  disc, 
ask  him  to  read  the  smallest  type  he  can  with  the 

'  naked  eye,  record  this  vision  to  compare  it  with 
the  final  correction.  Now  place  a  plus  .50  in  the 
trial  frame,  and  if  the  patient  is  myopic  he  will 
say,  ''I  cannot  see  so  well,"  or  in  other  words,  will 
not  be  able  to  read  the  same  line  as  before.  Then 
draw  his  attention  to  the  astigmatic  wheel  and 
say,"  can  you  see  the  spokes  in  the  wheel,  and  do 


OPTICAL  DICTIONARY.  189 

they  look  equally  clear?''  If  he  cannot  see  any  of 
the  spokes  clearly  enough  to  count  the  lines,  re- 
move a  quarter  D.  of  the  plus  sphere.  If  with 
this  he  fail  to  see  any  of  the  spokes  clearly, 
remove  the  other  quarter  from  the  trial  frame. 
If  none  of  the  spokes  are  yet  clear,  begin  with  the 
weakest  minus  sphere  and  gradually  increase 
same  a  quarter  D.  at  a  time  until  one  or  more 
spokes  come  up  clearly.  If  they  all  appear  clear 
at  the  same  time  there  is  no  astigmatism,  and  we 
turn  to  the  reading  chart  and  give  him  the  weak- 
est minus  sphere  that  will  allow  him  to  read  the 
best.  This  would  be  his  correction.  On  the 
other  hand,  if  there  is  astigmatism,  the  wheel  will 
not  come  up  equally  clear,  but  some  spokes  will 
be  plainer  than  others.  The  main  point  is  not 
to  increase  the  minus  sphere  after  one  or  more 
spokes  appear  clearly;  for  instance,  we  will  say 
we  have  on  a  minus  1  sphere  and  the  patient  tells 
us  that  he  cannot  count  any  lines  in  any  of  the 
spokes  as  yet.  We  add  to  this  sphere  a  minus 
25,  which  will  make  it  minus  1.25,  and  if  he  says 
''Now  I  can  see  one  spoke  clearly,"  and  it  runs 
from  12  to  6,  this  is  the  time  to  begin  with  the 
weakest  minus  cylinder,  placing  the  axis  at  right 
angles  to  the  plain  spoke,  increasing  its  strength 
until  you  find  the  weakest  that  makes  the  wheel 
look  uniform  in  density.  In  this  case  we  will 
say  that  it  required  a  minus  .75  cylinder,  that 
cylinder  combined  with  the  sphere  already  in  the 
frame  will  be  the  correction,  which  will  read  as 
follows: — 1.25  sph.  O  — .75  cyl.  ax.  180. 

Trichiasis  (trick-i'-a-sis).     That  condition  where  the 
/  eyelashes,  instead  of  extending  forward,  are  di- 
rected more  or  less  backward,  so  as  to  come  in 


190  LEWIS  POCKET 

contact  with  the  cornea.  Trichiasis  causes  a  con- 
tinual irritation  of  the  eyeball,  due  to  the  action 
of  the  cilia  (eyelashes);  there  is  photophobia, 
lachrymation,  and  a  constant  sense  of  a  foreign 
body  in  the  eye.  The  cornea  itself  suffers  consid- 
erable injury. 

Trichitis  (trick-i'-tis) .  Inflammation  of  the  root  of 
the  eyelashes. 

Trichosis  (tri-ko'-sis).  A  disease  of  the  hair.  (See 
Trichiasis.) 

Trichroic  (tri-kro'-ik) .  That  which  exhibits  three 
different  colors  in  three-  different  positions. 

Trichromatic  (tri-kro-mat'-ik) .  That  which  has 
three  colors. 

Triplet.     A  combination  of  three  lenses. 

Triplopia  (trip-lo'-pi-ah) .  That  condition  in  which 
there  are  three  images  of  the  same  object  formed 
upon  the  retina. 

\  Trochlea  (troch'-le-ah) .     A  pulley-shaped  part,  such 
^    as  that  through  which  the  superior  oblique  mus- 
cle passes. 

Trochlearis  (troch-le-a'-ris).  That  which  refers  to 
the  superior  oblique  muscle. 

Tumor  (tu'-mor).  A  swelling.  A  growth  of  new 
tissue,  differing  in  structure  from  the  part  on 
which  it  grows,  not  the  result  of  inflammation. 

Tunic.  Coat  or  covering.  The  eye  has  three  tunics; 
from  without  inward  they  are:  first,  sclerotic  and 
cornea;  second,  choroid,  ciliary  body,  and  iris; 
third,  the  retina.. 


OPTICAL  DICTIONARY.  191 

Tunica.  Same  as  tunic.  T.  adnata,  that  portion  of 
the  conjunctiva  which  comes  in  contact  with  the 
eyeball. 

Tiitam'ina  Oculi.  The  protecting  appendages  of 
the  eye,  such  as  the  eyelids  and  lashes. 

Typhlorogy.     A  treatise  on  blindness. 

Typlilo'sis.     Blindness. 

Tylosis  (ty-lo'-sis).  A  thickened,  ulcerated  condi- 
tion of  the  lid  margins  after  ulceration. 


U  leer.     An  open  sore,  other  than  a  wound. 

Ulceration  (ul-ser-a'-shun) .     Formation  of  an  ulcer. 

Umbo  (um'-bo).  The  apex,  pointed  or  protuberant 
part  of  any  substance.  When  applied  to  lenses, 
the  extreme  elevation  of  a  convex  spherical  lens, 
or  it  may  apply  to  the  center  of  a  concave  spheri- 
cal lens. 

Umbra.     A  shadow. 

Undula'tion.     A  wave-like  motion  in  any  medium. 

Un'dulatory  Theory.  A  theory  that  light,  heat  and 
electricity  move  with  a  wave-like  motion. 

Uniaxial  (u-ne-ak'-se-al) .     That  which  has  but  one 

axis. 

Unioc'ular.     Only  one  eye. 

Uremia  (u-re'-me-ah).  Blood-poisoning  from  re- 
tained urinary  excretions. 


192  LEWIS  POCKET 

UTaef ormis  (u-ve-f  or'-mis) .  The  middle  coat  of  the 
choroid.  » 

Uvea.      The  choroid,  ciHary  body,  and  iris  together. 

Uveal  Coat.  The  second  tunic  or  coat  of  the  eye- 
ball. 

Uveitis  (u-ve-i'-tis) .  That  condition  in  which  the 
uvea  is  inflamed.    Iritis. 

Uveal  (u'-ve-al).  That  which  refers  to  the  vascular 
layer  of  the  choroid  coat,  or  the  ciliary  body  and 
iris. 


"y  .     Abbreviation  for  vision. 

Vein.  A  vessel  which  conveys  blood  toward  the 
heart. 

Visibility  (vis-i-bil'-i-ty) .  That  which  has  the  capa- 
city of  being  seen. 

Vision.  The  ability  of  the  organ  of  sight  (the  eye) 
to  recognize  surrounding  objects.  Double  v.,  (see 
Diplopia).  Binocular  v.,  seeing  an  object  with 
both  eyes  at  the  same  time  without  diplopia. 
Monocular  v.,  the  act  of  seeing  with  only  one  eye. 

Visual.  Pertaining  to  vision  or  sight.  V.  Angle,  an 
angle  formed  by  lines  drawn  from  the  extreme 
edges  of  an  object  which  cross  at  the  nodal  point. 
V.  Axis,  a  line  drawn  from  the  macula  lutea 
through  the  nodal  point  to  the  object  looked  at. 
V*  Field,  the  space  containing  all  objects  visible 
while  the  eye  is  in  a  fixed  position.  V.  Purple, 
purple  pigment  to  be  found  in  the  retina,  which 
is  bleached  by  the  action  of  light. 


OPTICAL  DICTIONARY.  193 

Visual  Acuteness.  The  amount  seen  by  the  naked 
>  eye  if  emmetropic;  if  ametropic,  while  wearing 
his  correction.  The  smaller  the  objects  that  the 
eye  can  distinguish,  or  the  greater  the  distance  at 
which  an  object  of  given  size  can  be  seen,  the 
greater  is  the  acuity  of  vision  the  eye  possesses. 

Vitreous  ( vit'-re-ous) .  A  transparent  fluid  occupy- 
ing the  posterior  and  interior  four-fifths  of  the 
eye. 

Vitreous  Humor.  A  transparent,  colorless,  gelatin- 
ous mass  which  fills  the  posterior  cavity  of  the 
eye.  It  somewhat  resembles  the  white  of  an  egg 
and  is  surrounded  by  the  hyaloid  membrane. 
(See  Anatomy.)     Its  index  of  refraction  is  1.33. 

Virtual  Focus,     An  imaginary  or  negative  focus. 

Von  Graefe's  Sign.  That  condition  where  the  lid 
fails  to  move  downward  with  eyeball  in  exoph- 
thalmic goiter. 


W  all-eye.  This  term  has  several  meanings.  It 
generally  refers  to  white  opacities  of  the  cornea 
or  a  pale  blue  iris.  Sometimes  divergent  strabis- 
mus. 

AV'ave  Theory.     The   theory    that   light   travels   in 
waves  instead  of  rays.     (See  Light). 

Vrink.  The  act  of  opening  and  closing  the  eyelid 
suddenly. 

Winker.     (See  Eyelash.) 

Worsted  Test.  The  common  test  employed  for 
color-blindness. 


lit 


194  LEWIS  POCKET 

.-^Xanthelasma  (zan-thel-as'-mah).  That  condition 
in  which  there  is  a  flat  tumor  of  a  dirty  sulphur- 
yellow  color  which  projects  a  little  above  the 
skin  of  the  lid.  It  is  found  most  frequently  on 
the  upper  and  lower  lids  at  the  inner  angle  of  the 
eye. 

Xanthocyanopia  (zan-tho-cy-an-o'-pi-ah).  That  con- 
dition in  which  there  is  an  inability  to  perceive 
red  and  green  colors. 

Xanthoma  (zan-tho'-mah).  A  yellowish  new  growth 
on  the  skin. 

Xanthophane.  A  condition  in  which  objects  appear 
yellow. 

Xeroma  (ze-ro'-mah).  That  condition  where  the 
conjunctiva  is  abnormally  dry. 

Xerophthalmia  (ze-rof-thal'-mi-ah).  Conjunctivitis 
with  atrophy  and  no  liquid  discharge. 

Xerosis  (ze-ro'-sis).     Abnormal  dryness  of  the  eye. 


i  ellow  Spot.     The  macula  lutea. 

Young-Helmholtz  Theory.  The  theory  that  color 
vision  depends  on  three  sets  of  retinal  fibers  which 
correspond  to  the  colors  red,  violet,  and  green. 


/      ^eiss's   Glands.      The   sebaceous   or  sweat  glands 
located  at  the  free  border  of  the  eyelids. 


OPTICAL  DICTIONARY.  195 

Zinn*s  Ligament.  A  circular  ligament  at  the  optic 
foramen  from  which  arises  the  recti  muscles  of 
the  eye;  the  ligament  itself  is  attached  to  the 
bone  and  allows  the  optic  nerve  to  pass 
through  its  center. 

Zone.     A  girdle  or  belt. 

Zonula.  A  very  small  membrane  surrounding  a 
body.     A  small  zone. 

Zonule  of  Zinn.  The  suspensory  ligament  of  the 
eye-lens.     It    consists    of    delicate    fibers    which 

'  take  their  origin  from  the  inner  surface  of  the 
ciliary  body,  beginning  at  the  ora  serrata.  The 
fibers  are  in  contact  with  the  surface  of  the  cili- 
ary body,  but  leave  it  at  the  apices  of  the  ciliary 
processes,  and,  becoming  free,  divide  and  pass  over 
to  the  edge  of  the  lens,  thus  forming  the  anterior 
and  posterior  suspensory  ligaments.  These  liga- 
ments are  attached  to  the  capsule  of  the  lens 
with  which  they  become  fused.  The  space,  tri- 
angular in  shape,  included  between  tlie  fibers  of 
the  zonule  or  suspensory  ligaments  and  the  edge 
of  the  lens  is  called  the  Canal  of  Petit. 

Just  outside  of  the  optic  nerve,  where  it  pierces 
the  eyeball,  is  found  a  circle  of  blood-vessels  giving 
a  free  supply  to  the  optic  sheath  at  this  point,  and 
sending  branches  into  the  substance  of  the  nerve 
to  supply  nutrition.  This  circle  is  known  as  the 
Circulus  of  Zinn  or  sometimes  called  a  Zone  of 
Zinn. 

Zonulitis.    Inflammatiou  of  the  Zonule  of  Ziun, 


196  LEWIS  POCKET 

RULES  TO  BE  REMEMBERED. 

No.  1.  No  eye  should  be  allowed  to  use  accommo- 
dation at  20  feet  or  more. 

No.  2.  Always  give  a  hyperope  the  strongest  plus 
that  will  not  blur  his  best  distant  vision. 

No.  3.  Give  a  myope  the  weakest  minus  that  will 
give  him  best  vision.  Never  put  minus  where  it 
does  not  show  returns. 

No.  4.  After  putting  the  patient  in  the  fog,  place 
the  axis  of  your  minus  cylinder  at  right  angles  to 
the  plainest  line  seen. 

No.  5.  Correct  presbyopia  after  correcting  dis- 
tant vision. 

No.  6.  Before  testing  for  muscle  trouble  correct 
the  ametropia. 


A.    FEW    QUESTIONS    WITH    THEIR    ANSWERS. 

1.  Q.    What  governs  the  passage  of  light  through 

any  transparent  media? 
A.    Density. 

2.  Q.    On  what  does  the  visual  angle  depend  for 

its  existence? 
A.    The  size  and  distance  of  the  object. 

3.  Q.    What  three  laws  accompany  refraction? 
A.    Reflection,  absorption  and  dispersion. 

4.  Q.    In  what  three  ways  can  an  incident  ray  be 

disposed  of? 
A.    Reflected,  absorbed  or  refracted. 

5.  Q.    What  three  laws  must  be  brought  into  play 

in  order  to  obtain  distinct  binocular  vision 
at  various  distances?  ' 

A.   Refraction,   accommodation  and   converg- 
ence, 


OPTICAL  DICTIONARY.  197 

6.  Q.   Why  is  it  necessary  for  the  aqueous  humor 

to  be  thinner  than  the  vitreous  humor  and 
yet  have  the  same  density? 
A.    To  allow  freedom  of  movement  to  the  iris. 

7.  Q.    Why  is  accommodation  and  convergence  so 

closely  associated? 
A,    Because   they   are   both   operated   by    the 
same   nerve,   and  must   both    be    brought 
into  play  for  the  same  purpose. 
8o    Q.    What  lens  represents  the  focal  strength  of 
the  dioptric  system  of  the  eye? 
A.    From  62  to  65 -D.  plus. 
9.    Q.    When  is  a  lens  periscopic? 

A.    When  it  is  minus  on  one  side  and  plus  on 
the  other. 

10.  Q.    What  are  objective  and  subjective  symp- 

^     toms? 
A.    Objective  symptoms  are  what  the  operator 
detects    without    questioning    the    patient. 
Subjective  symptoms  are  those  described  by 
the  patient. 

11.  Q.    Why  does  amblyopia  cause  convergent  stra- 

bismus? 
A.    In  order  to  prevent  the  amblyopic  eye  from 
interfering  with  the  vision  of  the  good  eye, 
the  patient  turns  the  eye  toward  the  nose. 

12.  Q.    Why  do  we  add  and  subtract  from  retino- 

scopic  findings? 
A.    To  place  the  patient's  far  point  at  20  feet. 
3.    Q.    Why  is  the  concave  retinoscope  superior  to 

the  plane? 
A.    Because   a   concave   retinoscope   combined 

with  a  plus  20-D.  lens  can  be  used  as  an 

ophthalmoscope,  while  a  plane  retinoscope 

cannot. 


198  LEWIS  POCKET 

14.  Q.    What  lens  can  be   combined  with  plus   I 

sphere  combined  with  plus  1  cylinder,  axis 
90,  that  will  increase  the  cylinder  and  de- 
crease the  sphere? 
A.    Any  minus  cylinder  under  2  diopters  with 
its  axis  at  180. 

15.  Q.    What  is  false  myopia,  and  how  is  it  pro 

duced? 
A.    A  spasm  of  accommodation  in  emmetropia 
will  cause  the  eye  to  appear  myopic,  and  is 
brought  about  by  continual  strain  at  close 
,     work,  exophoria  or  hyperopia. 


Points  one  should  be  familar  with  before  attempt- 
ing a  State  Examination. 

1.  Mechanical  parts  of  frames  and  guards 
for  mounting  lenses;  making  face  measurements 
for  same;  truing  up  bent  frames  and  guards;  ad- 
justing same  to  different  persons. 

2.  The  common  shapes  and  forms  and  dioptric 
values  of  lenses  of  different  kinds;  submitting 
ten  different  kinds  to  applicants  for  determina- 
tion  of   these   qualities. 

3.  Practical  fitting  with  trial  case,  a  test  of 
the  applicant's  practical  ability  to  go  through 
these  tests  and  accurately  fit  different  classes 
of   cases  with  lenses. 

4.  Shadow  testing,  with  or  without  an  instru- 
ment; the  actual  doing  of  this  work  and  deter- 
mining the  error  of  refraction  by  the  method. 
The  mirror  or  instrument  preferred  may  be  used. 

5.  Muscle  testing,  and  the  use  of  muscle 
testing  devices;  a  test  of  the  applicant's  ability 
to  make  these  tests  and  draw  correct  conclu- 
sions from  them  and  their  showings. 


OPTICAL  DICTIONARY.  19& 

6.  The  proper  use  of  different  optical  instru- 
ments used  to  measure  the  refraction  of  the  eyes 
or  any  surface,  or  the  power  of  the  muscles  of 
the  eyes. 

7.  Questions  on  the  anatomy  and  physiology 
of  the  eyes,  including  muscles,  nerves,  tissues 
and  their  functions. 

8.  Questions  on  refraction  of  lenses,  transpo- 
sition, conjugate  foci,  image  forming,  and  the 
media  of  the  eye. 

9.  Questions  in  optometry,  the  fitting  of 
theoretical  cases  embracing  all  conditions  of 
refraction  met  in  practice. 

10.  Questions  on  the  muscles  and  their 
anomalies,  and  the  meaning  of  the  different 
results  obtained  in  practical  testing. 

11.  Questions  relative  to  cases  that  lenses 
do  not  fully  correct;  internal  or  external  indica- 
tions of  disease. 

EXAMINATION    QUESTIONS. 

1.  What  is  refraction,  reflection,  diffraction? 

2.  What  are  the  principal  laws  of  refraction, 
reflection? 

3.  Give  a  brief  description  of  the  wave  theory 
of  light  transmission. 

4.  What  is  a  ray  of  light?  a  pencil? 

5.  What  do  you  understand  by  the  following: 
The  optical  center  of  a  lens,  the  center  of  curva- 
ture, the  normal  to  a  surface? 

6.  Describe  a  lens;  name  the  kinds,  and 
explain  how  each  influences  parallel  rays  of 
light,  together  with  ametropic  conditions  each 
is  used  to  correct. 


200  LEWIS  POCKET 

7.  What  do  we  understand  by  the  terms 
focus,  virtual  focus  and  principal  focus? 

8.  Name  three  kinds  of  mirrors  relative  to 
their  curvature  of  surface  and  tell  how  each 
influences  parallel  Hght  rays. 

9.  Define  the  incident,  the  refracted,  the 
reflected  ray. 

10.  Define  a  one  dioptre  lens,  and  tell  how 
you  would  differentiate  between  a  plus  and 
minus  lens;  also  between  a  sphere  and  a  cylinder. 

11.  What  is  the  nodal  point;  the  principal 
and  secondary  axis  of  a  lens? 

12.  Which  ray  passes  through  the  lens  un- 
changed,  and  along  what  lines   does  it  travel? 

13.  What  is  an  angle;  right  angle;  sine  of  the 
angle;  an  arc;  and  tell  which  is  the  greater  angle, 
one  whose  arc  measures  -t5^,    or  one  of  90^'. 

14.  Define  the  visual  angle  and  give  the  size 
of  its  angle  when  required  to  show  20-20  vision 
at  30  feet. 

15.  Define  the  term  radius  of  curvature; 
and  explain  the  difference  between  the  expres- 
sions *' greater  curvature"  and  ^'lesser  curva- 
ture;" also  state  which  lens  has  the  greater 
curvature,  — ^5D.  or  — 8D. 

16.  Name'  three  causes  which  contribute  to 
the  determination  of  the  focal  point  of  a  lens. 

17.  How  would  you  proceed  to  find  the 
optical  center  of  a  lens,  the  axis  of  a  cylinder, 
the  base  apex  line  of  the  prism?  . 

18.  Define  the\term  '* conjugate  foci"  and 
calculate  the  distance  of  the  object  when  the 
image  is  formed  at  15  centimeters,  a  -f-  5  D, 
intervening. 


OPTICAL  DICTIONARY.  201 

19.  Give  the  table  for  linear  measure  in  the 
Metric  System;  the  equivalents  of  the  meter  and 
centimeter  in  inches. 

20.  If  the  curve  on  one  surface  of  a  bi-convex 
lens  is  on  a  13J  inch  radius  and  the  other  on  a 
40  inch  radius,  what  is  the  power  of  the  lens? 

21.  Why  does  a  distant  object,  seen  through 
a  plus  lens,  seem  to  grow  in  size  as  the  lens  is 
pushed  forward?  and  what  is  the  action  of  a  minus 
lens  under  similar  conditions? 

22.  Transpose  the  following:  — 2  S.  O  -f  .75 
C.  ax.  75.  Write  two  prescriptions  for  a  case 
of  astigmatism,  the  vertical  meridian  — 3.75  D. 
myopic,  and  horizontal  — 75  D.  myopic. 

23.  Describe  the  difference  between  the  image 
formed  by  the  entire  lens  and  one  in  which  the 
rays  must  also  pass  through  a  pinhole  diaphragm. 
State  the  clinical  signification  when  the  pinhole 
test  fails  to  improve  vision. 

24.  What  is  an  image,  and  how  is  it  formed, 
and  state  the  position  it  assumes  on  the  retina 
relative  to  the  object? 

25.  Describe  a  prism;  and  tell  how  the  unit 
of  measure,  the  prism  dioptre,  is  obtained. 

26.  By  what  means  and  how  do  we  obtain 
the  spectrum,  and  what  does  it  teach  us? 

27.  What  is  chromatic  aberration?  spherical 
aberration? 

28.  Which  glass  has  the  greater  dispersive 
power — crown  or  flint?  and  which  of  the  compo- 
nent rays  of  white  light  is  influenced  most  pow- 
erfully and  which  the  least  by  the  laws  of  refrac- 
tion? 

29.  Give  a  brief  description  of  the  retinoscope 
and  the  principles  involved. 


202  LEWIS  POCKET 

30.  Define  the  character  of  the  shadow  and 
the  direction  of  its  movements,  in  simple  hyper- 
metropia,  simple  myopia  and  astigmatism,  with 
plane  mirror. 

31.  How  many  methods  are  there  for  examin- 
ation of  the  retina  by  means  of  the  opthalmo- 
scope,  and  in  what  particulars  do  they  differ? 

32.  In  the  direct  method  with  the  ophthal- 
moscope, if  you  are  — 2  D.  myopic  and  you  get 
the  best  view  of  the  fundus  through  the  sight- 
hole,  no  lens  intervening,  and  accommodation 
at  rest,  what  is  your  patient's  condition  of  re- 
fraction? 

33.  When  the  eye  ground  is  examined  with 
the  ophthalmoscope,  under  what  conditions  are 
each  of  the  tunics  visible? 

34.  What  is  the  course  of  light  rays,  reflected 
from  the  posterior  part  of  the  eye  (the  eye  being 
at  rest),  in  myopia,  hypermetropia  and  emme- 
tropia? 

35.  What  do  you  understand  by  decentra- 
tion  of  lens  and  its  relations  to  the  adjustment 
of  spectacles? 

36.  Define  pupillary  distance  and  tell  how 
you  would  measure  same. 

37.  How  would  you  proceed  to  measure  for 
spectacles?  name  the  principal  measurements 
involved. 

38.  What  constitutes  the  dioptric  system  of 
the  eye? 

39.  Give  the  average  dimensions  of  the  emme- 
tropic eye  and  the  dioptric  value  of  lens  neces- 
sary to  neutralize  one  mm.  increase  in  length 
of  eye  beyond  that  in   emmetropia. 


OPTICAL  DICTIONARY.  203 

40.  Define  the  optic  axis  of  the  eye;  the  visuai 
line  and  the  angle  gamma. 

41.  What  do  you  understand  by  static  and 
dynamic  refraction  of  the  eye?  punctum  proxi- 
mum  and  punctum  remotum? 

42.  Describe  accommodation  and  name  the 
several  anatomical  parts  co-ordinating  during 
the  act. 

43.  How  is  the  accommodation  influenced 
by  age?  Give  the  powers  of  accommodation  at 
40,  45,  50,  and  70  years  of  age. 

44.  What  is  range  or  amplitude  of  accommo- 
dation, and  what  do  you  understand  by  relative 
range  of  accommodation  and  relative  range  of 
convergence? 

45.  How  may  spasm  of  accommodation  affect 
the  refraction  of  the  eye  and  complicate  the  tests 
therefor?  Differentiate  between  tonic  and  clonic 
spasms  of   accommodation. 

46.  Give  some  of  the  symptoms  of  hyper- 
metropia  where  this  condition  exists  in  a  mild 
degree. 

47.  What  is  hypermetropia?  Name  the  con- 
ditions of  the  dioptric  system  that  may  be  the 
immediate  cause  of  this  error  in  refraction. 

48.  What  is  the  state  of  refraction  in  myopia? 
Name  the  conditions  of  the  dioptric  system  that 
may  be  the  immediate   cause   of  this  anomaly. 

49.  What  are  the  different  tests  for  hyper- 
metropia,   myopia   and   astigmatism? 

50.  How  would  you  proceed  to  diagnose  an 
error  of  refraction? 

51.  Describe  the  cornea  and  its  curvature  of 
surface  in  detail.  Give  its  index  of  refraction 
and  name  the  dioptric  value  of  one  mm.  varia- 


204  LEWIS  POOKET 

tion  in  radius  of  curvature  of  any  one  meridian 
of   the   cornea. 

52.  What  is  astigmatism,  and  into  how  many 
classes  and  subdivisions  is  regular  astigmatism 
divided? 

53.  What  is  irregular  astigmatism,  and  what 
parts  of  the  dioptric  system  are  at  fault? 

54.  What  is  keratometry? 

55.  Name  the  following  radii  of  curvature: 
The  anterior  and  posterior  surfaces  of  cornea 
and  lens,  also  the  distance  of  the  anterior  princi- 
pal focus  from  summit  of  cornea  and  posterior 
principal  focus  from  the  nodal  point. 

56.  What  is  conical  cornea  and  its  effect  on 
the  refraction? 

57.  What  constitutes  perfect  binocular  vision? 
What  is  the  fusion  sense? 

58.  Define  orthophoria  and  give  the  tech- 
nical terms  for  each  condition  of  heterophoria 
and  heterotropia;  and  name  the  tests  for  hetero- 
phoria. 

59.  Define  abduction,  adduction,  sursum- 
duction  and  torsion;  and  name  the  muscles  func- 
tioning  in   each   movement. 

60.  How  would  you  differentiate  between 
concomitant  and  paralytic  strabismus?  and  how 
do  they  differ  in  regard  to  subjective  symptoms? 

61.  Define  paresis  and  paralysis,  and  tell  how 
you  would  diagnose  either  condition. 

62.  What  is  diplopia,  and  the  cause?  Define 
homonymous  and  heteronymous  diplopia  and 
describe  the  orientation  of  the  false  image  in 
either  condition  of  diplopia. 


OPTICAL  DICTIONARY.  205 

63.  Name  the  intrinsic  and  extrinsic  muscles 
of  the  eye,  and  the  nerves  supplying  innerva- 
tions to  each. 

64.  Define  convergence  and  its  relation  to 
accommodation.  How  would  a  prism  base  in 
affect  convergence,  base  out? 

65.  Name  the  muscles  affected  in  each  eye 
by  the  following  prescription:  O.  D.  +  3.50  D., 
O.  S.  +  7.50  D.,  decentered  2mm.  in  at  meridian 
135.  Denominate  prismatic  value  at  primary 
position  of  eyes. 

66.  What  is  the  iris?  Name  its  functions, 
also  define  mydriasis  and  miosis,  naming  at  least 
three  drugs  producing  the  former  and  two  the 
latter  condition. 

67.  Define  anisometropia  and  state  how  this 
condition,  when  marked,  complicates  the  correc- 
tion of  refractive  defects. 

68.  Describe  the  crystalline  lens;  name  and 
describe  its  functions;  give  its  index  of  refraction 
and  the  refractive  effect  of  extraction. 

69.  Describe  the  character  of  the  vitreous 
and  its  functions,  and  state  whether  or  not  the 
index  of  refraction  is  in  excess  of  that  of  the 
crystaline  lens. 

70  What  is  the  aqueous  and  its  functions? 
how  is  it  divided  and  how  does  its  index  of  re- 
fraction compare  with  that  of  the  cornea? 

71.  What  is  the  Capsule  of  Tenon  and  its 
functions?  What  are  the  check  ligaments  and 
their  functions?     What   is   the   trochlea? 

72.  Describe  the  optic  orbit  in  detail. 

73.  Describe  the  function  of  the  lids  and 
name  their  muscles,  with  the  nerves  dominating 


206  LEWIS  POCKET 

each.     What  are  the  cartilages  and  their  purpose? 
What  are  the  canthi? 

74.  Describe  the  meibomian  glands  and  their 
functions. 

75.  Of  what  does  the  lachrymal  apparatus 
consist? 

76.  In  what  way  do  the  tears  escape  from 
the  conjunctival  sac?  and  with  what  cavitiss  is 
this  duct  continuous? 

77.  Describe  the  ciliary  muscle,  its  ligarneii  r-e 
and  functions. 

78.  Describe  the  sclera,  and  name  it^  tum:^ 
tions. 

79.  Describe  the  choroid,  and  name  its  f u'&c-  • 
tions. 

80.  Describe  the  circulatory  system  of  the 
eye,  and  name  the  principal  arteries  and  veins. . 

81.  Describe  the  nervous  system  of  the  eye. , 

82.  What  i«  the  character  of  the  retina  audi 
its  relations  to  the  optic  nerve? 

83.  What  do  you  understand  by  acutenessi 
of  vision?.  Name  and  describe  the  point  of  most  I 
acute  vision  in  the  eye,  and  name  the  functions 
of  the  peripheral  portion  of  the  retina. 

84.  What  is  asthenopia  and  what  causes  itf  I 

85.  Describe  leukoma  and  opacity. 

86.  Name  the  principal  diseases  of  the  cptiC: 
nerve. 

87.  Describe  the  objective  and  subjectiva 
symptoms  of  glaucoma  and  name  certain  drugs 
that  have  a  tendency  to  precipitate  an  attack  of  i 
this  disease. 


OPTICAL  DICTIONARY.  207 

88.  What  is  the  ametropic  correction  for  a  patient, 
ige  twenty  years,  with  his  near  point  of  the  yertical 
neridian  at  eight  inches  and  the  near  point  of  the 
lorizontal  meridian  at  ten  inches? 

89.  What  is  the  correct  prescription  for  distance  for 
.  patient,  age  thirty  years,  looking  at  thirteen  inches, 
vith  his  focus  on  the  retina,  while  w^earing  a  +  2  sph. 

-  3  cyl.  ax.  90  and  using  two  diopters  of  accommoda- 
iion  ? 

90.  Does  an  emmetrope  always  have  normal  vision? 

91.  Put  the  following  prescription  back  to  the 
'tinoscopic  finding,  after  reversing  the  shadow  from 
1  inches: 

—  .50  sph.  O  —  .25  cyl.  ax.  60. 

92.  How  do  we  accommodate? 

93.  What  is  amblyopia?  myosis?  antimetropia? 

94.  W^hat  is  the  correction  for  an  eye,  with  its  f ar- 
oint at  eighty  inches  and  the  near-point  at  forty  inches 
•r  distance  and  reading  at  thirteen  inches? 

95.  If  a  patient  is  presbyopic  two  diopters  and  reads 
ithout  any  lens  at  thirteen  inches,  w^hat  is  his  error  of 
fraction  ? 

96.  What  causes  the  shadow  to  reverse  in  retinoscopy  ? 

97.  Do  we  always  improve  sight  in  correcting  hyper- 
etropia?     State  reason  for  your  answ^er. 

98.  How^  is  latent  hypermetropia  detected? 

99.  Put  the  following  prescription  up  in  toric  form, 
ing  a  plus  six  base  curve,  making  two  crosses  to  show 
ch  side  of  the  lens  and  the  power  needed  in  each  arm. 

+    3  sph.   O  —  2   cyl.   ax.  90. 

100.  When  a  prism  is  prescribed  for  constant  wear, 
e  the  eyes  parallel  to  each  other? 

101.  Place  a  lighted  candle  forty  inches  from  a  plus 
o  sphere,  then  a  distance  of  twenty  inches  to  a  plus 
e  sphere,  what  will  be  the  conjugate  foci? 


208  LEWIS  POCKET 

Appendix 

A.myosta'sia.      Nervous    tremor    of    the     musclel 
Amyosthe'nia.      Failure   of   muscular   strength. 
Anaphoria.      A  tendency  of  the  eyes  upward. 
Anatropia.      That  condition  in  which  the  eyes  tui 

up. 
An'nular    Muscle.      A   ring   shaped   muscle    (as   til 

sphincter  muscle  of  the  iris). 
Arach'noid    Sheath.     The    delicate    membrane     b 

tween  the  dura  mater  and  pia  mater  of  the  opt 

nerve  and  capsule  of  Tenon. 
Artificial     Pupil,      One      made      by      an     operatic 

(Iridectomy). 
Astigmom'eter.      An   intrument   for    measuring   s 

tigm^atism. 
Astig'mometry.     The     study     of     measurement 

astigmatism. 
Atax'ia.      Failure  of  muscles  to  coordinate. 
Atypic  Hypermetropia  (at-ip'-ik).      Irregular  Hyp^ 

metropia  caused  by  tumors  behind  the  eye,  e 

erting  such  a  pressure  on  the  posterior  pole  th 

the  region   of  the   macula  is  pushed  in   front  ' 

the  principal   focus,   the   eye  thus  becoming  h 

peropic.      ]t   may    be   caused   by    detachment! 

the  retina  in  the  region  of  the  macula. 
Atypic     Myopia     (at-ip'-ik).      Progressive     Myopj 

caused  by  the  elongation  of  the  eye. 
Axial    Ametropia.      Ametropia    that    is  ^  caused 

the  length  of  the  eyeball  on  the  optic  axis. 
Axis  of  a  Mirror.      A  line  which  strikes  the  cent 

of    curvature    at   right   angles   to   the   surface! 

called  its   axis. 

Jjase  Curve.     The  meridian  of  least  refraction, 

the  toric  side  of  a  lens. 
Basedow's   Disease    (See   exophthalmic   goiter). 
Bi-Spherical.     A  lens  with  a  sphere  on  both  sidi 


OPTICAL  DICTIONARY.  209 

Bruch's   Glands.     The   lymph-follicles   of   the    con- 

juctiva  of  the  lower  eyelid. 
3ruch*s  Membrane.     The  inner  layer  of  the  choroid 

coat  of  the  eye. 
Sruch's  Muscle.     See  Ciliarj'-  Muscle. 

L'analic'ulus.     A  small  canal  or  channel. 

(^ap'illary  (hair  like).  Any  one  of  the  little  vessels 
which  conduct  the  blood  from  the  arteries  to 
the  veins. 

i^ardinal  Points.  Points  which  play  an  important 
part  in  the  course  of  light  through  a  spherical 
surface.  There  are  four  in  number.  The  two 
principal  foci  and  the  two  nodal  points.  The 
first  principal  focus  is  the  point  from  which  light 
r-ays  emanate  and  pass  through  a  spherical  lens 
and  emerge  parallel  to  its  principal  axis.  The 
second  principal  focus  is  the  point  where  the 
emergent  rays  cross  each  other  when  the  incident 
rays   have   been    parallel    to    the    principal    axis. 

Caustic  Curve  (kaus'-tik).  A  curve  to  which  the 
rays  of  light  reflected  or  refracted  by  another 
curve  are  tangent. 

^elluHtis  (sel-u-li'-tis).  Inflammation  of  the  loose 
tissues  of  the  orbit. 

Centrifugal  (sen-trif'-u-gal).  Tending,  or  causing, 
to  recede  from  the  center. 

Centrifugal  Impression,  An  impression  sent  from  a 
nerve  center  outwards  to  a  muscle  or  muscles  by 
which  motion  is  produced. 

Ciliary  Processes.  The  radiating  circular  folds 
composed  of  a  connective  tissue  stroma,  which 
pass  up  over  the  ciliary  body.  There  are  abont 
sixty  or  seventy  in  number. 

Conjugate  Deviation.  The  deviation  of  both  eyes 
in  the  same  direction. 

Coquille-Plano  Lenses,  (plus  8D.  on  one  side  and 
minus  8D.  on  the  other).  MiCoquille  are  plus 
4D  on  one  side  and  minus  4D  on  the  other. 
They  are  nearly  always  colored. 


210  LEWIS  POCKET 

Corradiation  (kor-ra'-di-a'-shiin).  A  conjunction  oi 
concentration  of  rays  in  one  point. 

Corectomy  (ko-rek'-to-me) .     See  iridectomy. 

Cyst  (sist).  Any  sac  containing  a  liquid.  Derm-i 
oid  Cyst  is  congenital.  It  is  a  painless,  unin-i 
flammed  spheroidal  mass,  situated  generallji 
at  the  outer  angle  of  the  orbit,  on  a  level  with  thn 

•    outer  end  of  the  eyebrow. 

Jjecomposition  of  Light.  If  parallel  rays  of  sum 
light  pass  through  a  prism,  it  is  not  only  re- 
fracted, but  it  is  also  decomposed  into  its  variousi 
colors.  This  is  due  to  the  unequal  •  refrangi, 
bility  of  the  different  colored  rays  which  formi 
white  light,  the  violet  being  refracted  the  most 
and  the  red  the  least,  thus  forming  the  spectrumj 

Deor'sumvergens.     Downward  turning  of  the  eye* 

Dura  Mater.  The  outermost  membrane  of  the  brainy 
spinal  cord,  optic  nerve  and  capsule  of  Tenon. 

Dural  Sheath.  The  external  covering  of  the  optici 
nerv^e. 

Dynameter  (dy-nam'-e-ter).  An  instrument  for 
determining  the  magnifying  power  of  telescopes, 

Dynamometer  (dy'-na-mom'-e-ter).  An  instru- 
ment for  measuring  force  or  power;  especially 
the  muscular  power. 

Dynamometry  (dy'-na-mom'-e-try).  The  process* 
of  measuring  force  while  doing  work. 

Dyslexia  (dis-lex'-se-ah).  Inability  to  read  caused 
by  a  disease  of  the  brain.  Vision  is  good  but  the 
power  to  read  is  wanting. 

Dysopsy  (dys-op'-sy).     Dimness  of  vision. 

xlimphyse'ma.  The  infiltration  of  air  into  the  cellu-* 
lar  tissues  of  the  orbit.  May  be  caused  by  rupturf 
of  the  lachrymal  sac. 

Ephidro'sis.  An  excessive  secretion  of  the  sweat 
glands  of  the  eyelids.  It  causes  itching,  irrita- 
tion and  inflammation  of  the  skin  and  con- 
junctiva,    it  is  difficult  to  cure. 


OPTICAL  DICTIONARY.  211 

ithelio^ma.      Cancer  composed  largely  of  epithel- 
%l  cells   and  is  the   most  frequent  of  malignant 

Irowths  affecting  the  eyelid.     It  seldom  appears 

|efore  the  age  of  forty. 
in'sic.      Of    exterior    origin.     E.     Muscles      are 
lose  on  the  outside  of  the  organ. 
Ground.     The  inside  and  back  part  of  the  eye. 

the  Fundus. 

r  alse  Image.  The  image  seen  with  the  deviating 
eye. 

^ascia  (fash'-e-ah").  A  band  or  sheet  of  tissue  con- 
necting and  investing  muscles. 

^ocal  Planes.  Straight  lines  through  the  foci 
perpendicular  to  the  principal  axis. 

^ocus.  The  point  produced  by  light  coming  to 
or  going  from  a  point.  First  Principal  Focus 
is  at  the  point  the  light  leaves  as  divergent 
rays  and  emerges  from  the  optical  system  as 
parallel  to  the  principal  axis.  The  Second 
Principal-  Focus  is  the  point  where  the  emergent 
rays  cross  each  other  when  the  incident  rays 
have  been  parallel  to  the  principal  axis.  Neg= 
ative  Focus  is  the  point  from  which  rays  of  light 
appear,  to,  but  do  not  come  from,  the  focus  of 
a  minus  lens.  Secondary  Focus.  Any  focus  of 
the   secondary  axis. 

hogging  System.  The  system  of  fitting  glasses  by 
first  making  the  patient  artificially  myopic  by 
means  of  plus  spheres,  if  they  are  not  already 
myopic,  the  idea  being  to  relax  all  accommoda- 
tion before  using  cylinders   (See  page   185), 

LxangMon  (gang'-gle-on).  A  collection  of  nerve  cells 
giving  off  nerve  fibers  in  one  or  more  directions. 
A  mass  of  vesicular  neurin  in  the  course  of  a  nerve, 
apart  from  the  brain  and  spinal  cord. 

ionorrhe'al  Ophthalmia.  The  most  acute  form  of 
purulent  conjunctivitis.  It  is  caused  b}^  the 
introduction  of  the  urethral  discharge  to  the  con- 
junctival  sac 


212  LEWIS  POCKET 

Jieterophoral'gia.     Pain  with  heterophoria. 
Histology  (his-tol'-o-je).     The  sdence  of  the  minute 

structure  and  composition  of  tissues. 
Hutchinson's   Pupil.     One   that  is   dilated   on   on© 

side. 


Inflection   (in-flek'-shun).     The  act  of  bending  im 
ward  or  that  state  of  being  bent  inward. 

Ijigamentum  Pectinatum.     The    ligaments    which 

pass    from    the    base    of   the   iris   to    the    cornea; 

Through  its  meshes  pass  Fontana's  spaces. 
Lymph  (limf).     A  pure  transparent  fluid  like  water? 

a   coagulable    fluid   in    animal   bodies,    contained 

in  bodies  called  lymphatics. 
Lymphatic     (Hm-fat'-ik).     Pertaining     to,     of     thd 

nature    of,    containing    or    conveying    lymph. 


JMedian.  Situated  in  the  middle.  The  Median 
line  refers  to  the  line  drawn  from  a  point  betweeif 
the  two  eyes  straight  forward  parallel  with  th(l 
two  eyes. 

Migraine  (mi-gran').  A  kind  of  sickness  or  nervoua 
headache,  usually  periodical  and  confined  to  th4 
side  of  the  head. 

Monochromatic  Light.  The  spectrum  is  formeo 
by  a  prism  dividing  Hght  into  its  seven  colorsi 
Such  light  is  called  Monochromatic  Light. 

Myitis    (mi-i'-tis).     Inflammation    of    the    muscles^ 

Myograph  (my'-o-graphV  An  instrument  for  re' 
cording  the  different  phases,  such  as  the  velocity: 
intensity,  &c.,  of  a  muscular  contraction,  witl 
the  aid  of  a  registering  apparatus. 

Myography  (my-og'-ra-phy).  A  description  of  mus4 
eels,  including  the  study  of  muscular  contraction 
with  the  aid  of  a  registering  apparatus. 


OPTICAL  DICTIONARY.  213 

Myology  (my-ol'-o-ji).  A  description  of  the  muscles 
of  the  human  body. 

Myologist  (my-ol'-o-gist).  One  skilled  in  that  part 
of    anatomy    which    treats    of    muscles. 

Myositis  (my'-o-si'-tis).  Inflammation  of  the  mus- 
cles. 

Muller's  Muscle,  Bands  of  circular  fibres  situated 
internal  to  the  radiating  muscles  in  the  ciliary 
bodv.  They  are  sometimes  called  the  *'ring 
muscle"  of  MuUer.  FIBRES  OF  MULLER— 
Are  the  radiating  fibres  which  pass  through  nearly 
the  entire  thickness  of  the  retina,  supporting  its 
different  layers  and  binding  them  together. 
They  form  at  one  end  the  membrana  limitans 
interna  and  at  the  other  end  the  externa. 

iVegative  Convergence.   The  act  of  turning  the  eyes 
outward  from  parallelism,  by  means  of  the  exter- 
nal recti  muscles  which  turn  the  eyes  outward. 
Neurasthenia    (nuras-then-i'-ah).      Exhaustion   of 
nerve  force. 

Nodal  Points  of  a  Lens.  The  two  points  of  the 
principal  axis,  so  situated  that  every  ray  which, 
before  being  refracted,  is  directed  toward  the 
first  of  them,  seems,  after  its  refraction,  to  come 
from  the  second  one,  and  take  a  direction  parallel 
to  that  which  it  had  at  first.  These  two  parallel 
rays  are  called  lines  of  direction,  and  act,  in  the 
combined  system,  the  same  part  as  the  line 
passing  through  the  nodal  point  of  a  single  re- 
fracting surface. 


tjcci pit o=Fron talis.  The  muscle  which  lifts  the 
eyebrows  upward.  Supplied  by  the  seventh 
nerve. 

Ocellus  \o-sel'-lus).     A  single  eye. 

Ophtharmia  Neonatorum.  A  form  of  purulent 
conjun^.tivitis  which  attacks  newly  born  children. 


'?14  LEWIS  POCKEr 

Optical  Center  of  a  Lens.  The  center  of  refraction 
It  is  found  by  making  two  parallel  radii  o 
curvature,  and  connecting  the  points  in  whicl 
they  meet  the  surfaces.  The  point  at  whicl 
this  line  cuts  the  principal  axis,  is  the  optica 
center. 

Optology   (op'-tol-o-ge).     See  optometry. 

Orb.     A  spherical  bodyo 


J:  aracente'sis.     Surgical    puncture   of   a  cavity. 

Perimetry  (pe-rim'-et-re).  Measurement  of  the 
visual  field. 

Pia  Mater.  The  innermost  membrane  of  the  brain 
and  spinal  cord,  optic  sheath  and  capsule  of 
Tenon. 

Polariscope.  An  instrument  used  in  showing  the 
phenomena  of  the  polarization  of  light. 

Principal  Planes.  Straight  lines  which  pass  through^ 
the  principal  points,  perpendicular  to  the  prin- 
cipal axis. 


jLvecomposition  of  Light.  The  reuniting  of  the  colors' 
of  the  spectrum  so  as  to  produce  white  Hght.  ^ 
It  is  done  by  placing  a  second  prism  exactly  Uke 
the  first  with  its  apex  turned  in  the  opposite 
direction.  The  light  will  be  recomposed  and  will 
emerge  from  the  second  prism  as  white  light. 

Ret'roscopic  Lens.  A  lens  that  is  tilted  inward 
at  the  top. 

Rules  for  Refraction.  In  order  to  obtain  the  radius 
of  curvature  of  any  media  multiply  the  focal 
length  desired  by  the  difference  of  the  index  in  the 
two  media. 


OPTICAL  DICTIONARY  2l4a 

TO  FIND  DIOPTRIC  VALUE  OF  ANY  SURFACE 

— Multiply  the  difference  of  the  index  of  refraction 
by  the  number  of  meter  curves  in  the  radius  of 
curvature  and  give  it  the  sign  of  the  curve  of  the 
denser  media.  Remember  two  meter  curves  in 
optics  means  one-half  and  three  meter  curves,  one- 
third  of  a  meter  and  so  on. 

TO    FIND    THE    ANGLE    OF    REFRACTION— 

Divide  the  angle  of  incidence  by  the  index  of  re- 
fraction of  the  second  media. 

{Sclerotomy  (skle-rot'-o-me).  Surgical  incision  of 
the  sclera. 

Se'cant   (In  Geometry).     A  line  that  cuts  another, 
or  divides  it  into  parts.      The  secant  of  a  circle 
■  is   a  hne   drawn   from  the   circumference   on   one 
side   to    a   point   on   the   outside   of   the    circum- 
ference on  the  other. 

Spectrum  (spec'-trum).  The  seven  primary  colors 
of  which  light  is  composed,  separated  after  pass- 
ing through  a  prism  together  form  the  solar 
spectrum.  The  colored  rays  of  which  light  is 
composed  become  separated  by  the  refraction 
of  a  prism  or  other  means.  Of  the  seven  colors 
which  form  the  spectrum  Violet  is  refracted  the 
most,  then  Indigo,  Blue,  Green,  Yellow,  Orange 
and  Red  the  least. 

Diffraction  spectrum  is  a  spectrum  produced  by 
diffraction. 

Chromatic  spectrum  is  the  visible  colored  rays 
of  the  solar  spectrum,  showing  the  seven  princi- 
pal colors  in  their  order  and  covering  the  larger 
portion  of  the  space  of  the  whole  spectrum. 
Supra-orbital  Foramen.  A  small  passage  in  the 
Supra-Orbital  Ridge  through  which  passes  the 
supra-orbital  nerve  (a  branch  of  the  fifth)  artery 
and  vein. 


2U5  LEWIS  POCKET 

TLangent  (tan'-gent).  (In  geometry).  A  line  which 
touches  a  curve  at  right  angles  to  its  surface, 
but  does  not  cut  it.  (In  trigonometry  the  tan- 
gent of  an  arc  is  a  right  angle  line  touching  the 
arc  at  one  extremity,  through  the  center  and 
through  the  other  extremity.) 

Tropom'eter.  An  instrument  for  measuring  the 
movements  of  the  eye. 


1 

OPTICAL  DICTIONARY.  215 

Transposition 

To  transpose  an  optical  prescription  is  to  change  the 
form  or  shape  of  the  lens  without  changing  its  optical 
value. 

Writing  a  prescription  from  a  cross  is  not  transposing. 
We  must  first  have  a  written  prescription  before  it  can 
be  transposed. 

In  order  that  you  may  be  able  to  give  your  patients 
glasses  which  give  them  the  best  possible  results,  it  will 
be  necessary  for  you  to  know  how  to  build  lenses  of 
different  shapes,   for  instance: 

Biconvex,  biconcave,  piano  convex,  piano  concave, 
periscopic  and  toric. 

Lenses  have  two  kinds  of  power,  minus  and  plus,— the 
former  being  thinner  in  the  center  and  the  latter  thinner 
at  the  edge.  These  lenses  can  be  made  up  as  a  sphere 
or  cylinder. 

A  sphere  is  a  lens  with  the  same  power  in  all  its  mer- 
idians. 

A  meridian  is  any  straight  line*  drawn  from  edge  to 
edge  over  its  optical  center. 


Cut  showing  how  the  meridians  of  an  eye  are  numbered 
from  right  to  left. 

The  optical  center  being  a  point  in  line  with  the 
thickest  part  of  a  plus  and  the  thinnest  part  of  a  minus 
lens. 

A  cylinder  is  a  lens  with  power  in  all  meridians  but 
one,  this  one,  having  no  power  and  is  called  its  axis. 
The  full  power  of  a  cylinder  is  always  found  at  right 
angles  to  its  axis. 

In  the  following  diagram  we  wHl  use  a  plus  four  sphere 
and  plus  four  cylinder  for  example: 


216 


LEWIS  POCKET 


^SSS^^^:;^ 


Notice  that  the  power  is  the  same  in  all  meridians 
of  a  sphere,  while  those  of  a  cylinder  vary  in  power. 

An  optical  prescription  is  nothing  more  than  an  order 
for  a  lens  of  a  given  power  and  shape,  and  when  it  is 
transposed,  the  shape  is  changed  but  not  its  optical 
value  (or  power);  for  instance,  we  take  the  following 
prescription : 

+  4  sph.  C  +  4  cyl.  ax.  180 
which  reads  plus  four  sphere  combined  with  a  plus  four 
cylinder,  axis  180.  The  optician,  on  receiving  this 
prescription,  will  grind  the  plus  four  sphere  on  one  side 
of  the  lens  and  a  plus  four  cylinder  on  the  other  and  cut 
it  out,  so  that  the  axis  of  the  cylinder  will  be  at  180 
degrees.  This  lens  being  plus  on  both  sides  is  known 
as  a  biconvex  lens. 


OPTICAL  DICTIONARY. 


217 


In  this  example  we  have  the  sphere  and  cylinder 
separated  and  together,  showing  their  combined  powers 
and  also  their  appearance  from  the  side.  It  should  be 
noted  that  the  sphere  does  not  change  its  value  under 
the  axis  of  the  cylinder,  thus,  forming  one  of  its  prin- 
cipal meridians. 

In  oixler  to  change  the  shape  of  this  lens,  we  must 
apply  the  following  rule: 

When  the  signs  of  the  sphere  and  cylinder  are  alike, 
that  is,  both  plus  or  both  minus,  add  the  values  together 
for  your  new  sphere  which  would  be  plus  eight,  then 
change  the  sign  of  your  cylinder,  which  makes  it  minus, 
but  do  not]  change  its  value.  Change  its  axis  90' 
taking  90  from  180  leaves  90,  thus  +  4  sph.  C  +  4  cyl. 
ax.  180  transposed  gives  you  +  8  sph.  C  —  4  cyl.  ax.  90. 

In  the  latter  prescription  you  have  what  is  known  as 
a  periscopic  lens,  one  side  plus  and  the  other  side  minus. 


.  This  shape  lens  is  much  preferred  by  the  Refractionist 
of  to-day  on  account  of  its  appearance  and  comfort 
to  the  patient. 


218 


LEWIS  POCKET 


Prescription  No.  2 :     —  3  sph.  C  —  2  cyl.  ax.  45. 
^Ihis  prescription  calls  for  —  3  sph.  and  a  —  2 
to  be  ground  together. 


l^sr 


This  diagram  shows  the  sphere  and  cylinder  separ 
and  together  and  their  appearance  from  the  side.  T 
lens  being  concave  on  both  sides  is  known  as  a  biconcj 
lens. 

In  order  to  make  it  periscopic  we  will  use  the  sa 
rule  as  before  as  the  signs  are  alike. 

Prescription :     —  3  sph.  O  —  2  cyl.  ax.    45. 

Transposed:      —  5  sph.  O  +  2  cyl.  ax.  135. 


OPTICAL  DICTIONARY. 


219 


That  is  when  the  signs  are  alike  add  the  values  to- 
i  sther  for  the  new  sphere,  which  will  be  —  5,  keeping  the 
lime  sign.  Change  the  sign  of  the  cylinder,  but  not 
s  value  and  change  its  axis  90' (by  adding  90  to  45). 
his  gives  us  an  axis  of  135'. 

I  When  your  prescription  reads  minus  and  plus  your 
i  ns  will  be  periscopic. 
A  prescription  thus:      +  5  sph.  C  —  4  cyl.  ax.  90,  will 


220 


LEWIS  POCKET 


be  ground,  and  in  order  fo  change  its  shape  it  must  t 
transposed  by  the  following  rule: 

When  the  signs  are  unlike  that  is,  one  plus  and  th 
other  minus,  subtract  for  your  new  sphere  thus: 

Example:  +  5  sph.  C  —  4  cyl.  ax.    90. 

Transposed:  +  1  sph.  C  +  4  cyl.  ax.  180. 
prefixing  the  sign  of  the  larger  number  and  change  t| 
sign  of  your  cylinder,  as  it  was  minus  we  make  it  pliji 
but  .do  not  change  its  value.  Char  e  the  axis  9| 
but  never  let  your  axis  run  above  180°.  If  your  a,^) 
was  above  90°  subtract  90°  from  it  and  you  have  rigl^ 
angles.  On  the  other  hand,  if  the  axis  was  below  1 
you  add  90°  to  it. 

Cross  cylinders    +  2  cyl.  ax.  180  C  +  3  cyl.    ax.  { 
in  this  prescription  we  have  two  cylinders  with  the 


axes  at  right  angles  to  each  other,  and  it  will  be  notici 
that  the  power  of  one  cylinder  lies  on  the  axis  of  t 
other.  In  this  way,  both  cylinders  keep  their  full  valil 
In  order  to  transpose  cross  cyhnders  into  spheii 
cylinders  (if  the  signs  are  alike)  take  the  smaller  cyhndi 
and  call  it  a  sphere  and  forget  its  axis  altogether.     Th^ 


OPTICAL  DICTIONARY. 


221 


;ake  the  difference  between  the  two  fo"  the  new  cylinder 
keeping  the  same  sign  and  axis. 

Example:  +  2  cyl.  ax.  180  C  +  3  cyl.  ax.  90. 

Transposed:       4-  2  sph.  C  +  1  cyl.  ax.  90. 


i%0' 


tL. 


+^ 


.±1 


^r 


% 


/io- 


Simple  Cylinders 

5!xample:      +2,  Cyhnder  axis  90  degrees. 
o 


t 


^■x_ 


jo- 


in order  to  transpose  this  prescription, just  call  the 
ylinder  a  sphere  of  the  same  value  and  combine  with 


222 


LEWIS  POCKET 


it  a  cylinder  of  the  same  value,  but  the  opposite  sign 
and  change  its  axis  90  degrees. 

Example:      +2,  Cylinder  axis  90  degrees. 

Answer:  +2,  Sphere,  combined  with  -  2,  Cylinde: 
axis  180  degrees. 


,/tr 


-A 


y^j 


-±i_ 


_±A- 


fSrO 


These  cuts  show  the  two  lenses  separate  and  coddi 
bined,  and  also  the  side  view. 

Neutralizing  is  doing  away  with  power  in  lenses  b 
the  act  of  placing  minus  and  plus  together.  Puttii 
lenses  with  the  same  sign  together,  their  values  ad( 
but  when  the  signs  are  different,  they  neutralize,  lea 
ing  the  difference  between  the  two,  with  the  sign  of  tl 
larger  number.  This  fact  must  be  remembered  wh( 
combining  lenses. 

Every  cylinder  has  one  flat  or  plain  meridian,  whi( 
is  called  its  axis.  Right  angles  to  its  axis  it  has  i 
greatest  curvature  (or  power),  and  whenever  a  cylind 
is  placed  on  a  sphere,  the  sphere  will  keep  its  value 
the  meridian  which  is  covered  by  the  axis  of  the  cylindC 
It  depends  upon  the  power  of  the  cylinder  what  chani 
will  be  made  in  th^  sphere  at  the  meridian,  right  ang^ 
to  the  axis  o^  t>      ylinder. 


OPTICAL  DICTIONARY. 


223 


To  write  a  prescription  from  a  cross,  take  the  power 
that  is  written  on  either  arm  with  the  same  sign  for 
your  sphere.  This  being  a  sphere,  it  will  put  the  same 
power  in  all  meridians  and  if  the  powers  on  the  arms 
of  the  cross  are  different,  it  cannot  correct  them  both, 
and  the  cyhnder  that  you  use  must  represent  the 
difference  between  the  two. 

In  this  case,  we  will  take  the  plus  two  for  the  sphere. 


+  3L 


/ro 


90' 


This  will  correct  the  vertical  or  ninetieth  meridian, 
while  it  will  under-correct  the  horizontal  by  two  diopters, 
which  will  call  for  a  plus  two  cylinder,  axis  ninety  de- 
grees, combined  with  the  plus  two  sphere. 

Example:  +2.00  Sphere  combined  with  +2.00 
Cylinder  axis  90  "degrees. 


+2. 


-±i 


-fa. 


/fo- 


±Jl 


90' 


224 


LEWIS  POCKET 


These  two  combined  together  give  us  tnc  w.amc 
power  as  that  called  for  on  the  cross. 

When  we  take  the  plus  four  for  the  sphere,  we  over- 
correct  the  vertical  meridian  by  two  diopters,  there- 
fore, it  will  be  necessary  to  combine  a  minus  two  cylin- 
der axis  180  degrees  in  order  to  get  the  desired  result. 


tli 


fOSph.  0-3Cyl.  ax.  90'  — 3  Sph.  O  +  5  Cyl.  ax.  90' 
+3  Sph.  o  +3  Cyl.  ax.  180     +2  Sph.  a -5  CyL  ax.  180' 


OPTICAL  DICTIONARY. 


225 


-  ^7S 


Jjo' 


+  3  Cyl.  ax.  45 

+  3  Sph.  0-3  Cyl.  ax.  135. 


90' 


3.75  Cyl.  ax.  180. 

3.75  Sph.  O  +  3.7f.    Cyl. 

ax.  90. 


The  Advantages  and  Make  of 
Toric  Lenses 

The  word  toric  was  taken  from  the  word  torus,  which 
means  in  architecture  the  large  semicircular  molding 
used  in  the  bases  of  columns,  and  the  term  is  appHed 
to  a  lens  having  curvature  in  all  meridians,  but  of 
different  amounts,  on  the  same  side  of  the  lens  with  its 
meridians  of  greatest  and  least  curvature  at  right  angles 
to  each  other.  The  other  side  of  the  lens  may  be  either 
piano,  concave  or  convex;  but  they  are  usually  made 
extra  deep  periscopic. 

To  give  an  idea  of  the  appearance  and  proper  uses 
of  such  lenses,  I  will  put  up  prescriptions  for  the  five 
subdivisions  of  ametropia  which  can  be  corrected  by 
lenses  in  toric  form.  This  can  best  be  explained  by 
diagrams. 

The  first  prescription  will  be  for  compound  hyperopic 
astigmatism  +  3  sph.  O  +  2  cyl.  ax.  90. 

This  lens  when  ground  must  refract  plus  three  diopters 
in  the  ninetieth  and  plus  five  diopters  in  the  one  hun_ 
dred  and  eightieth  meridians,  independent  of  its  shape* 


'226 


LEWIS  POCKET 
^3        . 


■J^ 


But  in  order  to  get  a  deep  periscopic  effect,  the  ad- 
vantage of  which  I  will  explain  later,  suppose  we  grind 
one  side  of  the  lens  thus: 

+  16 


•^<9. 


The  difference  between  the  curvatures  in  the  two 
meridians  gives  us  the  desired  value  of  the  cylinder 
and  on  the  other  side  we  will  grind  a  minus  three  sphere, 
which  will  neutralize  plus  three  from  all  meridians, 
leaving  the  lens  with  the  required  strength.  In  this 
lens  you  get  a  plus  sphere  and  a  plus  cylinder  and  at  the 
same  time,  if  a  cement  scale  is  required,  it  can  be  placed 
next  to  the  eye. 

The  next  is  a  prescription  for  simple  hyperopia  astig- 
matism:   +  3  cyl.  ax.  45. 


In  this  lens  you  require  plus  three  diopters  in  the 
one  hundred  and  thirty-fifth  meridian  and  no  power  in 


OPTICAL  DICTIONARY.  227 

the  forty-fifth  meridian.  The  difference  between  the  two 
being  three  diopters,  on  one  side  of  the  lens  we  will  grind 


plus  six  diopters  in  the  forty-fifth  meridian  and  plus 
nine  diopters  in  the  one  hundred  and  thirty-fifth  meri- 
dian, and  on  the  other  side  enough  minus  sphere  to 
neutralize  all  the  power  from  the,  forty-fifth  or  weakest 
meridian,  which  will  be  a  minus  six  sphere,  leaving  the 
lens  the  required  strength  and  shape. 

Prescription     for     compound    myopic     astigmatism: 
-  2  sph.  O  -  2  cyl.  ax.  180. 


-=:S. 


This  prescription  calls  for  a  minus  two  diopters  in  the 
one  hundred  and  eightieth  meridian  and  minus  four 
diopters  in  the  ninetieth;  the  value  of  the  cylinder  being 
two  diopters.  We  will  grind  on  one  side  minus  six  diopters 

-s. 


-6. 


/go- 


?0' 


228  LEWIS  POCKET 

in  the  one  hundred  and  eightieth  meridian  and  minus 
eight  diopters  in  the  ninetieth  meridan,  leaving  the 
cyHndrical  value  of  2  D.  between  the  two;  on  the 
other  side  we  grind  a  plus  four  sphere.  This  will  give 
us  the  desired  result  in  toric  form. 

Prescription    for    simple    myopic    astigmatism:   -  4 
cyl.  ax.   150. 


This  prescription  calls  for  minus  four  in  the  sixtieth! 
meridian  and  no  power  in  the  one  hundred  and  fiftieth! 
meridian;  the  difference  in  the  two  neutralizes  four 
diopters.     We  grind  on    one    side    minus   six  diopters 


V 

in  the  one  hundred  and  fiftieth  meridian  and  minus 
ten  diopters  in  the  sixtieth  meridian;  and  on  the  other 
side  we  grind  a  plus  six  sphere  which  will  neutrahze 
minus  six  diopters  from  all  meridians,  leaving  the  lens 
the  desired  strength  and  at  the  same  time  give  us  a 
deep  periscopic  lens. 

Prescription  for  mixed  astigmatism:  +  1  sph.  O 
-3  cyl.  ax.  90. 

This  prescription  calls  for  a  lens  that  is  plus  one 
diopter  in  the  ninetieth  meridian  and  minus  two  diopters 
in  the  one  hundred  and  eightieth  meridian. 


OPTICAL  DICTIONARY 


2^ 


no' 


90- 

The  difference  between  the  two  principal  meridians 
being  three  diopters,  we  will  grind  on  one  side  of  the 
lens  a  plus  six  diopter  in  the  one  hundred  and  eightieth 
meridian  and  plus  nine  diopters  in  the  ninetieth  meridian* 

+  9 


_±6, 


/StP/ 


On  the  other  side  we  will  grind  a  minus  eight  sphere 
which  will  neutralize  all  the  plus  from  the  one  hundred 
and  eightieth  meridian  (leaving  minus  two  power)  and 
plus  eight  from  the  ninetieth  meridian,  leaving  plus 
one  diopter,  the  desired  strength  required. 

It  will  be  noticed  that  I  have  used  a  plus  six  or  a 
minus  six  for  the  weakest  curve  on  the  toric  side.  This 
is  known  as  the  base  curve,  and  it  is  used  in  eighty  per 
cent,  of  the  toric  lenses  to-day,  as  this  permits  the  whole- 
sale houses  to  carry  a  stock  of  lenses  with  the  toric 
curves  already  ground,  thus  cheapening  the  prices  of 
toric  work. 


230 


LEWIS  POCKET 


Very  often  prescription  houses  receive  prescriptions 
calling  for  a  toric  sphere,  when  an  extra  deep  periscopic 
lens  is  required,  but  not  of  toric  shape,  which  would 
cost  four  times  the  price.  For  instance,  suppose  we 
require  a  plus  two  sphere  and  order  it  toric.  It  could 
be  made  plus  six  in  one  of  its  pricipal  meridians  and 
plus  eight  in  the  other. 


+Sr 


-t^ 


no' 


90 


And  on  the  other  side  minus  four  diopters  in  one 
meridian  and  minus  six  in  the  other  meridian.  The 
two  sides  combined  would  give  the  desired  result,  a 
plus  two  sphere,  but  it  would  be  a  very  expensive  form 
whereas  it  would  be  only  one-fourth  the  price  if  it  were 
to  be  ground  as  a  plus  six  sphere  on  one  side  and  minus 
four  sphere  on  the  other,  which  would  be  the  same 
dioptric  value.  It  is  never  advisable  to  order  real  toric 
spheres. 

When  lenses  of  high  power  are  required,  say  +16 
sph.  O  +  4  cyl.  ax.  90,  it  is  best  to  divide  the  power  in 
the  following  manner,  and  at  the  same  time  obtain  a 
toric  lens. 

The  prescription  calls  for  plus  sixteen  diopters  in 
the  vertical  meridian  and  plus  twenty  diopters  in  the 
one  hundred  and  eightieth  meridian. 


OPTICAL  DICTIONARY. 


2:^1 


■fXQ 


?o 


We  win  grind  on  one  side  of  the  lens,  plus  six  in  the 
90th  meridian  and  plus  ten  in  the  180th;  and  on  the 


/J>t> 


+t. 


-t/o. 


?o- 


other  side  a  plus  ten  sphere,  which  would  give  the  de- 
sired result.  The  same  may  be  done  with  strong  con- 
cave lenses,  this  making  them  biconcave. 

When  a  toric  lens  is  desired,  it  is  not  necessary  for 
the  refractionist  to  mention  the  curvature.  For  the 
sake  of  simplicity,  just  WTite  the  word  * 'toric"  beneath 
the  description  of  the  lenses  in  your  prescription.  Then 
write  the  prescription  in  the  usual  way. 

Toric  lenses  are  more  expensive  than  the  old  form 
of  lenses,  but  on  account  of  their  superiority  they  are 
coming  more  into  general  use. 

In  the  first  place  they  allow  a  greatly  enlarged  fiild 


or  vision,  by  allowing  the  patient  to  roll  the  eye  and 
at  the  same  time  see  through  the  edges  of  his  lens. 

With  lenses  of  the  ordinary  typo,  when  an  eye  turns 
it  looks  obliquely  through  them  and  obtains  a  prismatic 
effect  that  is  not  desired,  causing  the  image  to  be  more 


or  less  distorted  on  the  retina,  and  at  the  same  time  the 
patient  is  bothered  with  reflection  from  the  back  of  the 
lenses  of  objects  on  the  side.  With  deep  periscopic 
lenses,  the  curve  coincides  approximately  with  the 
arc  formed  by  the  eye  in  turning  and  the  eye  is  looking 
much  more  directly  through  the  lens  and  obtains  a 
much  larger  field  of  vision  without  the  prismatic  effect. 

The  diagrams  will  show  the  shape  of  the  two  kinds  of 
lenses  from  the  same  prescription,  +  2  sph.  O  -  1 
cyl.  ax.  90. 

Again,  the  edges  of  the  lenses  come  nearer  to  the  face, 
thus  adding  to  the  patient's  appearance.  The  result 
of  a  lens  of  this  description  is  freedom  and  comfort  to 
the  wearer,  so  much  so  that  the  extra  cost  should  not  be 
considered. 

When  a  cement  bifocal  is  required  the  toric  side  should 
always  be  plus,  so  that  a  minus  sphere  will  be  next  to  the 
eye,  on  which  the  scale  may  be  cemented. 


MEMORANDUM 


MEMORANDUM 


^^^■^  oS^        (fnr  *3/n»-  C*-"-*^ , 


-af> 


Ik.    i>0    '£  ^^^^€4.....,^     ^....^^J^'. 


>.,-.  ^"^^^ 


>f 


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